sshconfig

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README

sshconfig

GoDoc

This directory contains an implementation of a parser for OpenSSH's ssh_config file format.

The format and its parsing rules are slightly complicated.

Further reading:

This implementation

Implemented features:

  • All of the fields listed in the ssh_config(5) man page (and two additional Apple specific fields).
  • Partial Match directive support. Address, LocalAddress, LocalPort and RDomain are not implemented (because they require an established connection, which could be achievable later if needed).
  • Partial TOKENS expansion support. Like above, expanding some of the tokens would require an established connection to the host while parsing the config.
  • Include directive support, the parser will follow the Include directives as expected, in lexical order like the OpenSSH implementation. It will also detect circular includes.
  • Expansion of ~ and environment variables in the values for the supported fields listed on the man page.
  • Support for list modifier prefixes for fields like HostKeyAlgorithms or KexAlgorithms where you can use a + prefix to append to the default list, a - prefix to remove from the default list, or ^ to prepend to the default list.
  • Support and validation for "multistate fields" as they are called in OpenSSH's readconf.c which can act like booleans but can also contain other string values, such as yes, no, ask, always, none, etc.
  • A "strict" mode for supporting the IgnoreUnknown directive. When enabled, the parser will throw an error when it encounters an unknown directive. To enable, use the sshconfig.WithStrict() option when creating the parser.
  • The origin based value precedence is correctly implemented as described in the specification and as observed in the OpenSSH implementation.
  • Hostname canonicalization.
  • Original-like unquoting and splitting of values based on argv_split from the original C source converted to go.

Status

The parser has not been tested outside of the development environment at all yet.

If there's interest, the parser can be extracted from the rig repository and published as a separate module.

Usage

Typically you first create a parser via sshconfig.NewParser(nil) and then call Apply(obj) on it with a struct that you want to populate with the values for a given host from the system's ssh configuration files. You can also pass in an io.Reader to NewParser to read from a custom source instead of the default locations.

You can use the provided sshconfig.Config which includes all the known configuration fields or you can define a struct with only a subset of the fields. The object must have the same field names as listed in the ssh_config man page and at least a Host string field must exist for the parsing to work.

package main

import(
  "fmt"
  "github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
  // this will read the configurations from the default locations.
  parser, err := sshconfig.NewParser(nil) 
  // To read from a specific file or a string, pass in an io.Reader like:
  // parser, err := sshconfig.NewParser(strings.NewReader("Host example.com\nIdentityFile ~/.ssh/id_rsa\n"))

  if err != nil {
    panic(err)
  }
  host := &sshconfig.Config{}
  if err := parser.Apply(host, "example.com"); err != nil {
    panic(err)
  }
  fmt.Println(host.IdentityFile[0])
}

There's also a sshconfig.ConfigFor shorthand for when you're not expecting to need the configuration for more than one host:

package main

import(
  "fmt"
  "github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
  config, err := sshconfig.ConfigFor("example.com") 
  if err != nil {
    panic(err)
  }
  fmt.Println(config.IdentityFile[0])
}

You can output a ssh_config formatted string using sshconfig.Dump:

package main

import(
  "fmt"
  "github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
  config, err := sshconfig.ConfigFor("example.com") 
  if err != nil {
    panic(err)
  }
  str, err := sshconfig.Dump(config)
  fmt.Println(str)
}

This will output something like:

Host example.com
  AddKeysToAgent no
  AddressFamily any
  BatchMode no
  ...

Alternatives

Currently there seems to exist two alternatives:

  • kevinburke/ssh_config

    This is a somewhat complete implementation but there are several issues with it:

    • Does not support Match directives at all.
    • Does not support Hostname canonicalization, which requires an additional pass of parsing if the hostname gets changed.
    • Not all of the Boolean fields listed here are actually regular booleans. For example, ForwardAgent can be a path to an agent socket or an environment variable name.
    • Not all of the default values are correct or set. In fact, the list of defaults is from 2017. The default for IdentityFile is ~/.ssh/identity which started to phase out upon the release of OpenSSH 3.0 in 2001 which started defaulting to ~/.ssh/id_dsa. The list of defaultProtocol2Identities is not used and is missing a couple of entries.
    • It does not support the list modifier prefixes for fields like HostKeyAlgorithms or KexAlgorithms where you can use the + or ^ prefixes to append or prepend to the default list or the - prefix to remove from it.
    • When you need to know multiple settings for a given host, you have to query for each setting separately.
    • Values need to be unquoted and expanded and converted to correct types manually and values for white-space or comma separated list fields need to be split manually.
    • No expansion of ~/ or environment variables in the values (there's a pull request from 2021).
    • No expansion of the TOKENS (there's a pull request from 2022).
    • Doesn't seem to be actively maintained, there are open unanswered issues and unmerged pull requests from several years ago. See PR comment.

  • mikkeloscar/sshconfig

    A simplistic implementation that only supports a very limited subset of fields (Host, HostName, User, Port, IdentityFile, HostKeyAlgorithms, ProxyCommand, LocalForward, RemoteForward, DynamicForward, Ciphers and MACs). It implements even less features and quirks of the syntax. The GPL-3 license may be problematic for some.

Contributing

Issues and PRs are welcome. Especially ones that eliminate any of the //nolint comments.

Documentation

Overview

Package sshconfig provides a parser for OpenSSH ssh_config files as documented in the man page.

Implemented features:

  • Go mappings for all of the keys known to OpenSSH client (and two additional Apple specific fields from the Mac port).
  • Partial Match directive support. Address, LocalAddress, LocalPort and RDomain are not implemented because they require passing in a connection, which is not (yet?) implemented.
  • Partial token expansion support. Like above, expanding some of the tokens would require an established connection.
  • Include directive support, the parser will follow the Include directives in lexical order as specified in the spec.
  • Expansion of ~ and environment variables in the values where applicable (the enabled fields are listed in the man page).
  • Support for list modifier prefixes for fields like HostKeyAlgorithms or KexAlgorithms where you can use "+" prefix to append to default list, "-" to remove from the default list and ^ to prepend to the default list.
  • Support for boolean fields which can also have string values (yes, no, ask, always, none, etc.). These are not enforced or validated like in the OpenSSH implementation, if the field is a MultiStateBooleanValue, it will accept any string value, but Bool() will return the boolean value and an ok flag indicating if the value is one of the known boolean values.
  • "Strict" mode for supporting the IgnoreUnknown directive. When enabled, the parser will throw an error when it encounters an unknown directive. By default this is not enabled. To enable, use the [WithErrorOnUnknown] option when creating the parser.
  • The origin of each value can be determined.
  • The order based value precedence is correctly implemented as described in the specification.
  • Hostname canonicalization.
  • Original-like unquoting and splitting of values based on `argv_split` from the OpenSSH source converted to go.

Usage:

What you create a new Parser, what you get is not a key-value store that you can use to query values for keys. Upon initialization, the Parser reads in the ssh configuration files and creates an internal tree structure that will be iterated over for each host configuration object to be populated with values from the configuration.

The SSH configuration files do not define a list of hosts, it's not a phone-book. The configuration is a set of rules that match hostnames or other attributes like the username or the current local address and the settings are applied only when they match the current connection.

You can either use the full Config which includes all the known keys or you can define a struct with a subset of the keys that you are interested in.

Example 
package main

import (
	"log"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	// this will read the configurations from the default locations.
	parser, err := sshconfig.NewParser(nil)

	if err != nil {
		log.Fatal(err)
	}
	host := &sshconfig.Config{}
	if err := parser.Apply(host, "example.com"); err != nil {
		log.Fatal(err)
	}
}

Output:
Example (ConfigFromReader)

To read from a specific file or a string instead of the default files, pass in an io.Reader: 

package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	parser, err := sshconfig.NewParser(strings.NewReader("Host example.com\nIdentityFile id_example\n"))
	if err != nil {
		log.Fatal(err)
	}
	host := &sshconfig.Config{}
	if err := parser.Apply(host, "example.com"); err != nil {
		log.Fatal(err)
	}
	for _, identityFile := range host.IdentityFile {
		fmt.Println(identityFile)
	}
}

Output:

id_example
Example (Simple) 
package main

import (
	"fmt"
	"log"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	hostconfig, err := sshconfig.ConfigFor("example")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(hostconfig.Port)
}

Output:

22
Example (WithCustomConfigObject)

You can also use the parser to apply configuration values into your own custom Config object. 

package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	type customConfig struct {
		Host         string
		IdentityFile []string
	}

	// To read from a specific file or a string instead of the default files, pass in an io.Reader:
	parser, err := sshconfig.NewParser(strings.NewReader("Host example.com\nIdentityFile id_example\n"))
	if err != nil {
		log.Fatal(err)
	}
	host := &customConfig{}
	if err := parser.Apply(host, "example.com"); err != nil {
		log.Fatal(err)
	}
	fmt.Println(host.IdentityFile[0])
}

Output:

id_example

Index

Examples

Constants

This section is empty.

Variables

View Source 
var (
	// ErrSyntax is returned when the config file has a syntax error.
	ErrSyntax = errors.New("syntax error")

	// ErrInvalidObject is returned when the object passed to Apply is not compatible.
	ErrInvalidObject = errors.New("invalid object")

	// ErrNotImplemented is returned when encountering a ssh_config feature that has not been
	// implemented.
	ErrNotImplemented = errors.New("not implemented")
)

Exported errors.

Functions

func Dump 

func Dump(obj any) (string, error)

Dump an SSH configuration to a string.

Example: 

config, _ := sshconfig.ConfigFor("example.com")
dump, _ := sshconfig.Dump(config)
fmt.Println(dump)
// Output:
// Host example.com
// 	Hostname example.com
// 	User user
// 	..and so on

Types

type Config 

type Config struct {
	// Host is the host alias that is used to match suitable confirguration blocks, it holds
	// the value as it would have been given when running "ssh hostalias".
	//
	// It is used as the endpoint for the connection unless overridden by the Hostname
	// field.
	Host string

	// Specifies the user to log in as.  This can be useful when
	// a different user name is used on different machines.
	// This saves the trouble of having to remember to give the
	// user name on the command line.
	User string

	// Specifies the real host name to log into.  This can be
	// used to specify nicknames or abbreviations for hosts.
	// Arguments to Hostname accept the tokens described in the
	// "TOKENS" section.  Numeric IP addresses are also
	// permitted (both on the command line and in Hostname
	// specifications).  The default is the name given on the
	// command line.
	Hostname string

	// Controls whether explicit hostname canonicalization is
	// performed.  The default, no, is not to perform any name
	// rewriting and let the system resolver handle all hostname
	// lookups.  If set to yes then, for connections that do not
	// use a ProxyCommand or ProxyJump, ssh(1) will attempt to
	// canonicalize the hostname specified on the command line
	// using the CanonicalDomains suffixes and
	// CanonicalizePermittedCNAMEs rules.  If
	// CanonicalizeHostname is set to always, then
	// canonicalization is applied to proxied connections too.
	//
	// If this option is enabled, then the configuration files
	// are processed again using the new target name to pick up
	// any new configuration in matching Host and Match stanzas.
	// A value of none disables the use of a ProxyJump host.
	CanonicalizeHostname options.CanonicalizeHostnameOption

	// When CanonicalizeHostname is enabled, this option
	// specifies the list of domain suffixes in which to search
	// for the specified destination host.
	CanonicalDomains []string

	// Specifies the maximum number of dot characters in a
	// hostname before canonicalization is disabled.  The
	// default, 1, allows a single dot (i.e.
	// hostname.subdomain).
	CanonicalizeMaxDots int

	// Specifies whether to fail with an error when hostname
	// canonicalization fails.  The default, yes, will attempt
	// to look up the unqualified hostname using the system
	// resolver's search rules.  A value of no will cause ssh(1)
	// to fail instantly if CanonicalizeHostname is enabled and
	// the target hostname cannot be found in any of the domains
	// specified by CanonicalDomains.
	CanonicalizeFallbackLocal options.BooleanOption

	// Specifies rules to determine whether CNAMEs should be
	// followed when canonicalizing hostnames.  The rules
	// consist of one or more arguments of
	// source_domain_list:target_domain_list, where
	// source_domain_list is a pattern-list of domains that may
	// follow CNAMEs in canonicalization, and target_domain_list
	// is a pattern-list of domains that they may resolve to.
	//
	// For example,
	// "*.a.example.com:*.b.example.com,*.c.example.com" will
	// allow hostnames matching "*.a.example.com" to be
	// canonicalized to names in the "*.b.example.com" or
	// "*.c.example.com" domains.
	//
	// A single argument of "none" causes no CNAMEs to be
	// considered for canonicalization.  This is the default
	// behaviour.
	CanonicalizePermittedCNAMEs []string

	// Specifies whether keys should be automatically added to a
	// running ssh-agent(1).  If this option is set to yes and a
	// key is loaded from a file, the key and its passphrase are
	// added to the agent with the default lifetime, as if by
	// ssh-add(1).  If this option is set to ask, ssh(1) will
	// require confirmation using the SSH_ASKPASS program before
	// adding a key (see ssh-add(1) for details).  If this
	// option is set to confirm, each use of the key must be
	// confirmed, as if the -c option was specified to
	// ssh-add(1).  If this option is set to no, no keys are
	// added to the agent.  Alternately, this option may be
	// specified as a time interval using the format described
	// in the "TIME FORMATS" section of sshd_config(5) to
	// specify the key's lifetime in ssh-agent(1), after which
	// it will automatically be removed.  The argument must be
	// no (the default), yes, confirm (optionally followed by a
	// time interval), ask or a time interval.
	AddKeysToAgent options.AddKeysToAgentOption

	// Use apple's MPTCP. Mac only option.
	AppleMultiPath options.BooleanOption

	// When adding identities, each passphrase will also be stored in the user's keychain.
	// (this is a mac only option)
	UseKeychain options.BooleanOption

	// Specifies which address family to use when connecting.
	// Valid arguments are any (the default), inet (use IPv4
	// only), or inet6 (use IPv6 only).
	AddressFamily string // use enum setter

	// If set to yes, user interaction such as password prompts
	// and host key confirmation requests will be disabled.
	// This option is useful in scripts and other batch jobs
	// where no user is present to interact with ssh(1).  The
	// argument must be yes or no (the default).
	BatchMode options.BooleanOption

	// Use the specified address on the local machine as the
	// source address of the connection.  Only useful on systems
	// with more than one address.
	BindAddress string

	// Use the address of the specified interface on the local
	// machine as the source address of the connection.
	BindInterface string

	// Specifies which algorithms are allowed for signing of
	// certificates by certificate authorities (CAs).  The
	// default is:
	//
	// ssh-ed25519,ecdsa-sha2-nistp256,
	// ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
	// sk-ssh-ed25519@openssh.com,
	// sk-ecdsa-sha2-nistp256@openssh.com,
	// rsa-sha2-512,rsa-sha2-256
	//
	// If the specified list begins with a `+' character, then
	// the specified algorithms will be appended to the default
	// set instead of replacing them.  If the specified list
	// begins with a `-' character, then the specified
	// algorithms (including wildcards) will be removed from the
	// default set instead of replacing them.
	//
	// ssh(1) will not accept host certificates signed using
	// algorithms other than those specified.
	CASignatureAlgorithms []string // modifier prefixes

	// Specifies a file from which the user's certificate is
	// read.  A corresponding private key must be provided
	// separately in order to use this certificate either from
	// an IdentityFile directive or -i flag to ssh(1), via
	// ssh-agent(1), or via a PKCS11Provider or
	// SecurityKeyProvider.
	//
	// Arguments to CertificateFile may use the tilde syntax to
	// refer to a user's home directory, the tokens described in
	// the "TOKENS" section and environment variables as
	// described in the "ENVIRONMENT VARIABLES" section.
	//
	// It is possible to have multiple certificate files
	// specified in configuration files; these certificates will
	// be tried in sequence.  Multiple CertificateFile
	// directives will add to the list of certificates used for
	// authentication.
	CertificateFile []string // always append

	// Specifies whether and how quickly ssh(1) should close
	// inactive channels.  Timeouts are specified as one or more
	// "type=interval" pairs separated by whitespace, where the
	// "type" must be a channel type name (as described in the
	// table below), optionally containing wildcard characters.
	//
	// The timeout value "interval" is specified in seconds or
	// may use any of the units documented in the "TIME FORMATS"
	// section.  For example, "session=5m" would cause the
	// interactive session to terminate after five minutes of
	// inactivity.  Specifying a zero value disables the
	// inactivity timeout.
	//
	// The available channel types include:
	//
	// agent-connection
	// Open connections to ssh-agent(1).
	//
	// direct-tcpip, direct-streamlocal@openssh.com
	// Open TCP or Unix socket (respectively)
	// connections that have been established from a
	// ssh(1) local forwarding, i.e. LocalForward or
	// DynamicForward.
	//
	// forwarded-tcpip, forwarded-streamlocal@openssh.com
	// Open TCP or Unix socket (respectively)
	// connections that have been established to a
	// sshd(8) listening on behalf of a ssh(1) remote
	// forwarding, i.e. RemoteForward.
	//
	// session
	// The interactive main session, including shell
	// session, command execution, scp(1), sftp(1), etc.
	//
	// tun-connection
	// Open TunnelForward connections.
	//
	// x11-connection
	// Open X11 forwarding sessions.
	//
	// Note that in all the above cases, terminating an inactive
	// session does not guarantee to remove all resources
	// associated with the session, e.g. shell processes or X11
	// clients relating to the session may continue to execute.
	//
	// Moreover, terminating an inactive channel or session does
	// not necessarily close the SSH connection, nor does it
	// prevent a client from requesting another channel of the
	// same type.  In particular, expiring an inactive
	// forwarding session does not prevent another identical
	// forwarding from being subsequently created.
	//
	// The default is not to expire channels of any type for
	// inactivity.
	ChannelTimeout map[string]time.Duration // special key-value syntax

	// If set to yes, ssh(1) will additionally check the host IP
	// address in the known_hosts file.  This allows it to
	// detect if a host key changed due to DNS spoofing and will
	// add addresses of destination hosts to ~/.ssh/known_hosts
	// in the process, regardless of the setting of
	// StrictHostKeyChecking.  If the option is set to no (the
	// default), the check will not be executed.
	CheckHostIP options.BooleanOption

	// Specifies the ciphers allowed and their order of
	// preference.  Multiple ciphers must be comma-separated.
	// If the specified list begins with a `+' character, then
	// the specified ciphers will be appended to the default set
	// instead of replacing them.  If the specified list begins
	// with a `-' character, then the specified ciphers
	// (including wildcards) will be removed from the default
	// set instead of replacing them.  If the specified list
	// begins with a `^' character, then the specified ciphers
	// will be placed at the head of the default set.
	//
	// The supported ciphers are:
	//
	// 3des-cbc
	// aes128-cbc
	// aes192-cbc
	// aes256-cbc
	// aes128-ctr
	// aes192-ctr
	// aes256-ctr
	// aes128-gcm@openssh.com
	// aes256-gcm@openssh.com
	// chacha20-poly1305@openssh.com
	//
	// The default is:
	//
	// chacha20-poly1305@openssh.com,
	// aes128-ctr,aes192-ctr,aes256-ctr,
	// aes128-gcm@openssh.com,aes256-gcm@openssh.com
	//
	// The list of available ciphers may also be obtained using
	// "ssh -Q cipher".
	Ciphers []string // modifier prefixes, defaults need to be set first (oh no.)

	// Specifies that all local, remote, and dynamic port
	// forwardings specified in the configuration files or on
	// the command line be cleared.  This option is primarily
	// useful when used from the ssh(1) command line to clear
	// port forwardings set in configuration files, and is
	// automatically set by scp(1) and sftp(1).  The argument
	// must be yes or no (the default).
	ClearAllForwardings options.BooleanOption

	// Specifies whether to use compression.  The argument must
	// be yes or no (the default).
	Compression options.BooleanOption

	// Specifies the number of tries (one per second) to make
	// before exiting.  The argument must be an integer.  This
	// may be useful in scripts if the connection sometimes
	// fails.  The default is 1.
	ConnectionAttempts int

	// Specifies the timeout (in seconds) used when connecting
	// to the SSH server, instead of using the default system
	// TCP timeout.  This timeout is applied both to
	// establishing the connection and to performing the initial
	// SSH protocol handshake and key exchange.
	ConnectTimeout time.Duration

	// Enables the sharing of multiple sessions over a single
	// network connection.  When set to yes, ssh(1) will listen
	// for connections on a control socket specified using the
	// ControlPath argument.  Additional sessions can connect to
	// this socket using the same ControlPath with ControlMaster
	// set to no (the default).  These sessions will try to
	// reuse the master instance's network connection rather
	// than initiating new ones, but will fall back to
	// connecting normally if the control socket does not exist,
	// or is not listening.
	//
	// Setting this to ask will cause ssh(1) to listen for
	// control connections, but require confirmation using
	// ssh-askpass(1).  If the ControlPath cannot be opened,
	// ssh(1) will continue without connecting to a master
	// instance.
	//
	// X11 and ssh-agent(1) forwarding is supported over these
	// multiplexed connections, however the display and agent
	// forwarded will be the one belonging to the master
	// connection i.e. it is not possible to forward multiple
	// displays or agents.
	//
	// Two additional options allow for opportunistic
	// multiplexing: try to use a master connection but fall
	// back to creating a new one if one does not already exist.
	// These options are: auto and autoask.  The latter requires
	// confirmation like the ask option.
	ControlMaster options.ControlMasterOption // yes, no, ask, auto, autoask

	// Specify the path to the control socket used for
	// connection sharing as described in the ControlMaster
	// section above or the string none to disable connection
	// sharing.  Arguments to ControlPath may use the tilde
	// syntax to refer to a user's home directory, the tokens
	// described in the "TOKENS" section and environment
	// variables as described in the "ENVIRONMENT VARIABLES"
	// section.  It is recommended that any ControlPath used for
	// opportunistic connection sharing include at least %h, %p,
	// and %r (or alternatively %C) and be placed in a directory
	// that is not writable by other users.  This ensures that
	// shared connections are uniquely identified.
	ControlPath string // path, supports tokens and environment variables

	// When used in conjunction with ControlMaster, specifies
	// that the master connection should remain open in the
	// background (waiting for future client connections) after
	// the initial client connection has been closed.  If set to
	// no (the default), then the master connection will not be
	// placed into the background, and will close as soon as the
	// initial client connection is closed.  If set to yes or 0,
	// then the master connection will remain in the background
	// indefinitely (until killed or closed via a mechanism such
	// as the "ssh -O exit").  If set to a time in seconds, or a
	// time in any of the formats documented in sshd_config(5),
	// then the backgrounded master connection will
	// automatically terminate after it has remained idle (with
	// no client connections) for the specified time.
	ControlPersist options.ControlPersistOption

	// Specifies that a TCP port on the local machine be
	// forwarded over the secure channel, and the application
	// protocol is then used to determine where to connect to
	// from the remote machine.
	//
	// The argument must be [bind_address:]port.  IPv6 addresses
	// can be specified by enclosing addresses in square
	// brackets.  By default, the local port is bound in
	// accordance with the GatewayPorts setting.  However, an
	// explicit bind_address may be used to bind the connection
	// to a specific address.  The bind_address of localhost
	// indicates that the listening port be bound for local use
	// only, while an empty address or `*' indicates that the
	// port should be available from all interfaces.
	//
	// Currently the SOCKS4 and SOCKS5 protocols are supported,
	// and ssh(1) will act as a SOCKS server.  Multiple
	// forwardings may be specified, and additional forwardings
	// can be given on the command line.  Only the superuser can
	// forward privileged ports.
	DynamicForward []string // always append

	// Enables the command line option in the EscapeChar menu
	// for interactive sessions (default `~C').  By default, the
	// command line is disabled.
	EnableEscapeCommandline options.BooleanOption

	// Setting this option to yes in the global client
	// configuration file /etc/ssh/ssh_config enables the use of
	// the helper program ssh-keysign(8) during
	// HostbasedAuthentication.  The argument must be yes or no
	// (the default).  This option should be placed in the non-
	// hostspecific section.  See ssh-keysign(8) for more
	// information.
	EnableSSHKeysign options.BooleanOption

	// Sets the escape character (default: `~').  The escape
	// character can also be set on the command line.  The
	// argument should be a single character, `^' followed by a
	// letter, or none to disable the escape character entirely
	// (making the connection transparent for binary data).
	EscapeChar options.EscapeCharOption

	// Specifies whether ssh(1) should terminate the connection
	// if it cannot set up all requested dynamic, tunnel, local,
	// and remote port forwardings, (e.g. if either end is
	// unable to bind and listen on a specified port).  Note
	// that ExitOnForwardFailure does not apply to connections
	// made over port forwardings and will not, for example,
	// cause ssh(1) to exit if TCP connections to the ultimate
	// forwarding destination fail.  The argument must be yes or
	// no (the default).
	ExitOnForwardFailure options.BooleanOption

	// Specifies the hash algorithm used when displaying key
	// fingerprints.  Valid options are: md5 and sha256 (the
	// default).
	FingerprintHash options.FingerprintHashOption

	// Requests ssh to go to background just before command
	// execution.  This is useful if ssh is going to ask for
	// passwords or passphrases, but the user wants it in the
	// background.  This implies the StdinNull configuration
	// option being set to "yes".  The recommended way to start
	// X11 programs at a remote site is with something like ssh
	// -f host xterm, which is the same as ssh host xterm if the
	// ForkAfterAuthentication configuration option is set to
	// "yes".
	//
	// If the ExitOnForwardFailure configuration option is set
	// to "yes", then a client started with the
	// ForkAfterAuthentication configuration option being set to
	// "yes" will wait for all remote port forwards to be
	// successfully established before placing itself in the
	// background.  The argument to this keyword must be yes
	// (same as the -f option) or no (the default).
	ForkAfterAuthentication options.BooleanOption

	// Specifies whether the connection to the authentication
	// agent (if any) will be forwarded to the remote machine.
	// The argument may be yes, no (the default), an explicit
	// path to an agent socket or the name of an environment
	// variable (beginning with `$') in which to find the path.
	//
	// Agent forwarding should be enabled with caution.  Users
	// with the ability to bypass file permissions on the remote
	// host (for the agent's Unix-domain socket) can access the
	// local agent through the forwarded connection.  An
	// attacker cannot obtain key material from the agent,
	// however they can perform operations on the keys that
	// enable them to authenticate using the identities loaded
	// into the agent.
	ForwardAgent options.ForwardAgentOption

	// Specifies whether X11 connections will be automatically
	// redirected over the secure channel and DISPLAY set.  The
	// argument must be yes or no (the default).
	//
	// X11 forwarding should be enabled with caution.  Users
	// with the ability to bypass file permissions on the remote
	// host (for the user's X11 authorization database) can
	// access the local X11 display through the forwarded
	// connection.  An attacker may then be able to perform
	// activities such as keystroke monitoring if the
	// ForwardX11Trusted option is also enabled.
	ForwardX11 options.BooleanOption

	// Specify a timeout for untrusted X11 forwarding using the
	// format described in the "TIME FORMATS" section of
	// sshd_config(5).  X11 connections received by ssh(1) after
	// this time will be refused.  Setting ForwardX11Timeout to
	// zero will disable the timeout and permit X11 forwarding
	// for the life of the connection.  The default is to
	// disable untrusted X11 forwarding after twenty minutes has
	// elapsed.
	ForwardX11Timeout time.Duration

	// If this option is set to yes, remote X11 clients will
	// have full access to the original X11 display.
	//
	// If this option is set to no (the default), remote X11
	// clients will be considered untrusted and prevented from
	// stealing or tampering with data belonging to trusted X11
	// clients.  Furthermore, the xauth(1) token used for the
	// session will be set to expire after 20 minutes.  Remote
	// clients will be refused access after this time.
	//
	// See the X11 SECURITY extension specification for full
	// details on the restrictions imposed on untrusted clients.
	ForwardX11Trusted options.BooleanOption

	// Specifies whether remote hosts are allowed to connect to
	// local forwarded ports.  By default, ssh(1) binds local
	// port forwardings to the loopback address.  This prevents
	// other remote hosts from connecting to forwarded ports.
	// GatewayPorts can be used to specify that ssh should bind
	// local port forwardings to the wildcard address, thus
	// allowing remote hosts to connect to forwarded ports.  The
	// argument must be yes or no (the default).
	GatewayPorts options.BooleanOption

	// Specifies one or more files to use for the global host
	// key database, separated by whitespace.  The default is
	// /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
	GlobalKnownHostsFile []string // paths

	// Specifies whether user authentication based on GSSAPI is
	// allowed.  The default is no.
	GSSAPIAuthentication options.BooleanOption

	// Forward (delegate) credentials to the server.  The
	// default is no.
	GSSAPIDelegateCredentials options.BooleanOption

	// Indicates that ssh(1) should hash host names and
	// addresses when they are added to ~/.ssh/known_hosts.
	// These hashed names may be used normally by ssh(1) and
	// sshd(8), but they do not visually reveal identifying
	// information if the file's contents are disclosed.  The
	// default is no.  Note that existing names and addresses in
	// known hosts files will not be converted automatically,
	// but may be manually hashed using ssh-keygen(1).
	HashKnownHosts options.BooleanOption

	// Specifies the signature algorithms that will be used for
	// hostbased authentication as a comma-separated list of
	// patterns.  Alternately if the specified list begins with
	// a `+' character, then the specified signature algorithms
	// will be appended to the default set instead of replacing
	// them.  If the specified list begins with a `-' character,
	// then the specified signature algorithms (including
	// wildcards) will be removed from the default set instead
	// of replacing them.  If the specified list begins with a
	// `^' character, then the specified signature algorithms
	// will be placed at the head of the default set.  The
	// default for this option is:
	//
	// ssh-ed25519-cert-v01@openssh.com,
	// ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// ecdsa-sha2-nistp384-cert-v01@openssh.com,
	// ecdsa-sha2-nistp521-cert-v01@openssh.com,
	// sk-ssh-ed25519-cert-v01@openssh.com,
	// sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// rsa-sha2-512-cert-v01@openssh.com,
	// rsa-sha2-256-cert-v01@openssh.com,
	// ssh-ed25519,
	// ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
	// sk-ssh-ed25519@openssh.com,
	// sk-ecdsa-sha2-nistp256@openssh.com,
	// rsa-sha2-512,rsa-sha2-256
	//
	// The -Q option of ssh(1) may be used to list supported
	// signature algorithms.  This was formerly named
	// HostbasedKeyTypes.
	HostbasedAcceptedAlgorithms []string // modifier prefixes, defaults need to be set first

	// Specifies whether to try rhosts based authentication with
	// public key authentication.  The argument must be yes or
	// no (the default).
	HostbasedAuthentication options.BooleanOption

	// Specifies the host key signature algorithms that the
	// client wants to use in order of preference.  Alternately
	// if the specified list begins with a `+' character, then
	// the specified signature algorithms will be appended to
	// the default set instead of replacing them.  If the
	// specified list begins with a `-' character, then the
	// specified signature algorithms (including wildcards) will
	// be removed from the default set instead of replacing
	// them.  If the specified list begins with a `^' character,
	// then the specified signature algorithms will be placed at
	// the head of the default set.  The default for this option
	// is:
	//
	// ssh-ed25519-cert-v01@openssh.com,
	// ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// ecdsa-sha2-nistp384-cert-v01@openssh.com,
	// ecdsa-sha2-nistp521-cert-v01@openssh.com,
	// sk-ssh-ed25519-cert-v01@openssh.com,
	// sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// rsa-sha2-512-cert-v01@openssh.com,
	// rsa-sha2-256-cert-v01@openssh.com,
	// ssh-ed25519,
	// ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
	// sk-ecdsa-sha2-nistp256@openssh.com,
	// sk-ssh-ed25519@openssh.com,
	// rsa-sha2-512,rsa-sha2-256
	//
	// If hostkeys are known for the destination host then this
	// default is modified to prefer their algorithms.
	//
	// The list of available signature algorithms may also be
	// obtained using "ssh -Q HostKeyAlgorithms".
	HostKeyAlgorithms []string // modifier prefixes, defaults need to be set first

	// Specifies an alias that should be used instead of the
	// real host name when looking up or saving the host key in
	// the host key database files and when validating host
	// certificates.  This option is useful for tunneling SSH
	// connections or for multiple servers running on a single
	// host.
	HostKeyAlias string

	// Specifies that ssh(1) should only use the configured
	// authentication identity and certificate files (either the
	// default files, or those explicitly configured in the
	// files or passed on the ssh(1) command-line), even if
	// ssh-agent(1) or a PKCS11Provider or SecurityKeyProvider
	// offers more identities.  The argument to this keyword
	// must be yes or no (the default).  This option is intended
	// for situations where ssh-agent offers many different
	// identities.
	IdentitiesOnly options.BooleanOption

	// Specifies the Unix-domain socket used to communicate with
	// the authentication agent.
	//
	// This option overrides the SSH_AUTH_SOCK environment
	// variable and can be used to select a specific agent.
	// Setting the socket name to none disables the use of an
	// authentication agent.  If the string "SSH_AUTH_SOCK" is
	// specified, the location of the socket will be read from
	// the SSH_AUTH_SOCK environment variable.  Otherwise if the
	// specified value begins with a `$' character, then it will
	// be treated as an environment variable containing the
	// location of the socket.
	//
	// Arguments to IdentityAgent may use the tilde syntax to
	// refer to a user's home directory, the tokens described in
	// the "TOKENS" section and environment variables as
	// described in the "ENVIRONMENT VARIABLES" section.
	IdentityAgent options.IdentityAgentOption

	// Specifies a file from which the user's DSA, ECDSA,
	// authenticator-hosted ECDSA, Ed25519, authenticator-hosted
	// Ed25519 or RSA authentication identity is read.  You can
	// also specify a public key file to use the corresponding
	// private key that is loaded in ssh-agent(1) when the
	// private key file is not present locally.  The default is
	// ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk,
	// ~/.ssh/id_ed25519, ~/.ssh/id_ed25519_sk and
	// ~/.ssh/id_dsa.  Additionally, any identities represented
	// by the authentication agent will be used for
	// authentication unless IdentitiesOnly is set.  If no
	// certificates have been explicitly specified by
	// CertificateFile, ssh(1) will try to load certificate
	// information from the filename obtained by appending
	// -cert.pub to the path of a specified IdentityFile.
	//
	// Arguments to IdentityFile may use the tilde syntax to
	// refer to a user's home directory or the tokens described
	// in the "TOKENS" section.  Alternately an argument of none
	// may be used to indicate no identity files should be
	// loaded.
	//
	// It is possible to have multiple identity files specified
	// in configuration files; all these identities will be
	// tried in sequence.  Multiple IdentityFile directives will
	// add to the list of identities tried (this behaviour
	// differs from that of other configuration directives).
	//
	// IdentityFile may be used in conjunction with
	// IdentitiesOnly to select which identities in an agent are
	// offered during authentication.  IdentityFile may also be
	// used in conjunction with CertificateFile in order to
	// provide any certificate also needed for authentication
	// with the identity.
	IdentityFile []string // always append, supports none, paths, and tokens

	// Specifies a pattern-list of unknown options to be ignored
	// if they are encountered in configuration parsing.  This
	// may be used to suppress errors if contains options that
	// are unrecognised by ssh(1).  It is recommended that
	// IgnoreUnknown be listed early in the configuration file
	// as it will not be applied to unknown options that appear
	// before it.
	IgnoreUnknown []string // patterns

	// Specifies the IPv4 type-of-service or DSCP class for
	// connections.  Accepted values are af11, af12, af13, af21,
	// af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1,
	// cs2, cs3, cs4, cs5, cs6, cs7, ef, le, lowdelay,
	// throughput, reliability, a numeric value, or none to use
	// the operating system default.  This option may take one
	// or two arguments, separated by whitespace.  If one
	// argument is specified, it is used as the packet class
	// unconditionally.  If two values are specified, the first
	// is automatically selected for interactive sessions and
	// the second for non-interactive sessions.  The default is
	// af21 (Low-Latency Data) for interactive sessions and cs1
	// (Lower Effort) for non-interactive sessions.
	IPQoS []string // one or two values

	// Specifies whether to use keyboard-interactive
	// authentication.  The argument to this keyword must be yes
	// (the default) or no.  ChallengeResponseAuthentication is
	// a deprecated alias for this.
	KbdInteractiveAuthentication options.BooleanOption

	// Specifies the list of methods to use in keyboard-
	// interactive authentication.  Multiple method names must
	// be comma-separated.  The default is to use the server
	// specified list.  The methods available vary depending on
	// what the server supports.  For an OpenSSH server, it may
	// be zero or more of: bsdauth and pam.
	KbdInteractiveDevices []string // csv

	// Specifies the available KEX (Key Exchange) algorithms.
	// Multiple algorithms must be comma-separated.  If the
	// specified list begins with a `+' character, then the
	// specified algorithms will be appended to the default set
	// instead of replacing them.  If the specified list begins
	// with a `-' character, then the specified algorithms
	// (including wildcards) will be removed from the default
	// set instead of replacing them.  If the specified list
	// begins with a `^' character, then the specified
	// algorithms will be placed at the head of the default set.
	// The default is:
	//
	// sntrup761x25519-sha512@openssh.com,
	// curve25519-sha256,curve25519-sha256@libssh.org,
	// ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
	// diffie-hellman-group-exchange-sha256,
	// diffie-hellman-group16-sha512,
	// diffie-hellman-group18-sha512,
	// diffie-hellman-group14-sha256
	//
	// The list of available key exchange algorithms may also be
	// obtained using "ssh -Q kex".
	KexAlgorithms []string // modifier prefixes, defaults need to be set first, no none

	// Specifies a command to use to obtain a list of host keys,
	// in addition to those listed in UserKnownHostsFile and
	// GlobalKnownHostsFile.  This command is executed after the
	// files have been read.  It may write host key lines to
	// standard output in identical format to the usual files
	// (described in the "VERIFYING HOST KEYS" section in
	// ssh(1)).  Arguments to KnownHostsCommand accept the
	// tokens described in the "TOKENS" section.  The command
	// may be invoked multiple times per connection: once when
	// preparing the preference list of host key algorithms to
	// use, again to obtain the host key for the requested host
	// name and, if CheckHostIP is enabled, one more time to
	// obtain the host key matching the server's address.  If
	// the command exits abnormally or returns a non-zero exit
	// status then the connection is terminated.
	KnownHostsCommand string

	// Specifies a command to execute on the local machine after
	// successfully connecting to the server.  The command
	// string extends to the end of the line, and is executed
	// with the user's shell.  Arguments to LocalCommand accept
	// the tokens described in the "TOKENS" section.
	//
	// The command is run synchronously and does not have access
	// to the session of the ssh(1) that spawned it.  It should
	// not be used for interactive commands.
	//
	// This directive is ignored unless PermitLocalCommand has
	// been enabled.
	LocalCommand string // comment is part of value (oh no.)

	// Specifies that a TCP port on the local machine be
	// forwarded over the secure channel to the specified host
	// and port from the remote machine.  The first argument
	// specifies the listener and may be [bind_address:]port or
	// a Unix domain socket path.  The second argument is the
	// destination and may be host:hostport or a Unix domain
	// socket path if the remote host supports it.
	//
	// IPv6 addresses can be specified by enclosing addresses in
	// square brackets.  Multiple forwardings may be specified,
	// and additional forwardings can be given on the command
	// line.  Only the superuser can forward privileged ports.
	// By default, the local port is bound in accordance with
	// the GatewayPorts setting.  However, an explicit
	// bind_address may be used to bind the connection to a
	// specific address.  The bind_address of localhost
	// indicates that the listening port be bound for local use
	// only, while an empty address or `*' indicates that the
	// port should be available from all interfaces.  Unix
	// domain socket paths may use the tokens described in the
	// "TOKENS" section and environment variables as described
	// in the "ENVIRONMENT VARIABLES" section.
	LocalForward map[string]string // always appends, one pair per line like 8080 remote:80

	// Gives the verbosity level that is used when logging
	// messages from ssh(1).  The possible values are: QUIET,
	// FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and
	// DEBUG3.  The default is INFO.  DEBUG and DEBUG1 are
	// equivalent.  DEBUG2 and DEBUG3 each specify higher levels
	// of verbose output.
	LogLevel string // use enum setter

	// Specify one or more overrides to LogLevel.  An override
	// consists of a pattern lists that matches the source file,
	// function and line number to force detailed logging for.
	// For example, an override pattern of:
	//
	// kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
	//
	// would enable detailed logging for line 1000 of kex.c,
	// everything in the kex_exchange_identification() function,
	// and all code in the packet.c file.  This option is
	// intended for debugging and no overrides are enabled by
	// default.
	LogVerbose []string // patterns, openssh client specific

	// Specifies the MAC (message authentication code)
	// algorithms in order of preference.  The MAC algorithm is
	// used for data integrity protection.  Multiple algorithms
	// must be comma-separated.  If the specified list begins
	// with a `+' character, then the specified algorithms will
	// be appended to the default set instead of replacing them.
	// If the specified list begins with a `-' character, then
	// the specified algorithms (including wildcards) will be
	// removed from the default set instead of replacing them.
	// If the specified list begins with a `^' character, then
	// the specified algorithms will be placed at the head of
	// the default set.
	//
	// The algorithms that contain "-etm" calculate the MAC
	// after encryption (encrypt-then-mac).  These are
	// considered safer and their use recommended.
	//
	// The default is:
	//
	// umac-64-etm@openssh.com,umac-128-etm@openssh.com,
	// hmac-sha2-256-etm@openssh.com,
	// hmac-sha2-512-etm@openssh.com,
	// hmac-sha1-etm@openssh.com,
	// umac-64@openssh.com,umac-128@openssh.com,
	// hmac-sha2-256,hmac-sha2-512,hmac-sha1
	//
	// The list of available MAC algorithms may also be obtained
	// using "ssh -Q mac".
	MACs []string // modifier prefixes, defaults need to be set first, no none

	// Disable host authentication for localhost (loopback
	// addresses).  The argument to this keyword must be yes or
	// no (the default).
	NoHostAuthenticationForLocalhost options.BooleanOption

	// Specifies the number of password prompts before giving
	// up.  The argument to this keyword must be an integer.
	// The default is 3.
	NumberOfPasswordPrompts *int

	// Specifies whether ssh(1) should try to obscure inter-
	// keystroke timings from passive observers of network
	// traffic.  If enabled, then for interactive sessions,
	// ssh(1) will send keystrokes at fixed intervals of a few
	// tens of milliseconds and will send fake keystroke packets
	// for some time after typing ceases.  The argument to this
	// keyword must be yes, no or an interval specifier of the
	// form interval:milliseconds (e.g. interval:80 for 80
	// milliseconds).  The default is to obscure keystrokes
	// using a 20ms packet interval.  Note that smaller
	// intervals will result in higher fake keystroke packet
	// rates.
	ObscureKeystrokeTiming options.ObscureKeystrokeTimingOption

	// Specifies whether to use password authentication.  The
	// argument to this keyword must be yes (the default) or no.
	PasswordAuthentication options.BooleanOption

	// Allow local command execution via the LocalCommand option
	// or using the !command escape sequence in ssh(1).  The
	// argument must be yes or no (the default).
	PermitLocalCommand options.BooleanOption

	// Specifies the destinations to which remote TCP port
	// forwarding is permitted when RemoteForward is used as a
	// SOCKS proxy.  The forwarding specification must be one of
	// the following forms:
	//
	// PermitRemoteOpen host:port
	// PermitRemoteOpen IPv4_addr:port
	// PermitRemoteOpen [IPv6_addr]:port
	//
	// Multiple forwards may be specified by separating them
	// with whitespace.  An argument of any can be used to
	// remove all restrictions and permit any forwarding
	// requests.  An argument of none can be used to prohibit
	// all forwarding requests.  The wildcard `*' can be used
	// for host or port to allow all hosts or ports
	// respectively.  Otherwise, no pattern matching or address
	// lookups are performed on supplied names.
	PermitRemoteOpen []string

	// Specifies which PKCS#11 provider to use or none to
	// indicate that no provider should be used (the default).
	// The argument to this keyword is a path to the PKCS#11
	// shared library ssh(1) should use to communicate with a
	// PKCS#11 token providing keys for user authentication.
	PKCS11Provider string // none or path

	// Specifies the port number to connect on the remote host.
	// The default is 22.
	Port int

	// Specifies the order in which the client should try
	// authentication methods.  This allows a client to prefer
	// one method (e.g. keyboard-interactive) over another
	// method (e.g. password).  The default is:
	//
	// gssapi-with-mic,hostbased,publickey,
	// keyboard-interactive,password
	PreferredAuthentications []string // csv

	// Specifies the command to use to connect to the server.
	// The command string extends to the end of the line, and is
	// executed using the user's shell `exec' directive to avoid
	// a lingering shell process.
	//
	// Arguments to ProxyCommand accept the tokens described in
	// the "TOKENS" section.  The command can be basically
	// anything, and should read from its standard input and
	// write to its standard output.  It should eventually
	// connect an sshd(8) server running on some machine, or
	// execute sshd -i somewhere.  Host key management will be
	// done using the Hostname of the host being connected
	// (defaulting to the name typed by the user).  Setting the
	// command to none disables this option entirely.  Note that
	// CheckHostIP is not available for connects with a proxy
	// command.
	//
	// This directive is useful in conjunction with nc(1) and
	// its proxy support.  For example, the following directive
	// would connect via an HTTP proxy at 192.0.2.0:
	//
	// ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
	ProxyCommand string // none is a special value, comment is part of value

	// Specifies one or more jump proxies as either
	// [user@]host[:port] or an ssh URI.  Multiple proxies may
	// be separated by comma characters and will be visited
	// sequentially.  Setting this option will cause ssh(1) to
	// connect to the target host by first making a ssh(1)
	// connection to the specified ProxyJump host and then
	// establishing a TCP forwarding to the ultimate target from
	// there.  Setting the host to none disables this option
	// entirely.
	//
	// Note that this option will compete with the ProxyCommand
	// option - whichever is specified first will prevent later
	// instances of the other from taking effect.
	//
	// Note also that the configuration for the destination host
	// (either supplied via the command-line or the
	// configuration file) is not generally applied to jump
	// hosts.  ~/.ssh/config should be used if specific
	// configuration is required for jump hosts.
	ProxyJump []string // csv

	// Specifies that ProxyCommand will pass a connected file
	// descriptor back to ssh(1) instead of continuing to
	// execute and pass data.  The default is no.
	ProxyUseFdpass options.BooleanOption

	// Specifies the signature algorithms that will be used for
	// public key authentication as a comma-separated list of
	// patterns.  If the specified list begins with a `+'
	// character, then the algorithms after it will be appended
	// to the default instead of replacing it.  If the specified
	// list begins with a `-' character, then the specified
	// algorithms (including wildcards) will be removed from the
	// default set instead of replacing them.  If the specified
	// list begins with a `^' character, then the specified
	// algorithms will be placed at the head of the default set.
	// The default for this option is:
	//
	// ssh-ed25519-cert-v01@openssh.com,
	// ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// ecdsa-sha2-nistp384-cert-v01@openssh.com,
	// ecdsa-sha2-nistp521-cert-v01@openssh.com,
	// sk-ssh-ed25519-cert-v01@openssh.com,
	// sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
	// rsa-sha2-512-cert-v01@openssh.com,
	// rsa-sha2-256-cert-v01@openssh.com,
	// ssh-ed25519,
	// ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
	// sk-ssh-ed25519@openssh.com,
	// sk-ecdsa-sha2-nistp256@openssh.com,
	// rsa-sha2-512,rsa-sha2-256
	//
	// The list of available signature algorithms may also be
	// obtained using "ssh -Q PubkeyAcceptedAlgorithms".
	PubkeyAcceptedAlgorithms []string // preload defaults

	// Specifies whether to try public key authentication.  The
	// argument to this keyword must be yes (the default), no,
	// unbound or host-bound.  The final two options enable
	// public key authentication while respectively disabling or
	// enabling the OpenSSH host-bound authentication protocol
	// extension required for restricted ssh-agent(1)
	// forwarding.
	PubkeyAuthentication options.PubkeyAuthenticationOption

	// Specifies the maximum amount of data that may be
	// transmitted or received before the session key is
	// renegotiated, optionally followed by a maximum amount of
	// time that may pass before the session key is
	// renegotiated.  The first argument is specified in bytes
	// and may have a suffix of `K', `M', or `G' to indicate
	// Kilobytes, Megabytes, or Gigabytes, respectively.  The
	// default is between `1G' and `4G', depending on the
	// cipher.  The optional second value is specified in
	// seconds and may use any of the units documented in the
	// TIME FORMATS section of sshd_config(5).  The default
	// value for RekeyLimit is default none, which means that
	// rekeying is performed after the cipher's default amount
	// of data has been sent or received and no time based
	// rekeying is done.
	RekeyLimit options.RekeyLimitOption

	// Specifies a command to execute on the remote machine
	// after successfully connecting to the server.  The command
	// string extends to the end of the line, and is executed
	// with the user's shell.  Arguments to RemoteCommand accept
	// the tokens described in the "TOKENS" section.
	RemoteCommand string // comment is part of value

	// Specifies that a TCP port on the remote machine be
	// forwarded over the secure channel.  The remote port may
	// either be forwarded to a specified host and port from the
	// local machine, or may act as a SOCKS 4/5 proxy that
	// allows a remote client to connect to arbitrary
	// destinations from the local machine.  The first argument
	// is the listening specification and may be
	// [bind_address:]port or, if the remote host supports it, a
	// Unix domain socket path.  If forwarding to a specific
	// destination then the second argument must be
	// host:hostport or a Unix domain socket path, otherwise if
	// no destination argument is specified then the remote
	// forwarding will be established as a SOCKS proxy.  When
	// acting as a SOCKS proxy, the destination of the
	// connection can be restricted by PermitRemoteOpen.
	//
	// IPv6 addresses can be specified by enclosing addresses in
	// square brackets.  Multiple forwardings may be specified,
	// and additional forwardings can be given on the command
	// line.  Privileged ports can be forwarded only when
	// logging in as root on the remote machine.  Unix domain
	// socket paths may use the tokens described in the "TOKENS"
	// section and environment variables as described in the
	// "ENVIRONMENT VARIABLES" section.
	//
	// If the port argument is 0, the listen port will be
	// dynamically allocated on the server and reported to the
	// client at run time.
	//
	// If the bind_address is not specified, the default is to
	// only bind to loopback addresses.  If the bind_address is
	// `*' or an empty string, then the forwarding is requested
	// to listen on all interfaces.  Specifying a remote
	// bind_address will only succeed if the server's
	// GatewayPorts option is enabled (see sshd_config(5)).
	RemoteForward map[string]string // always append

	// Specifies whether to request a pseudo-tty for the
	// session.  The argument may be one of: no (never request a
	// TTY), yes (always request a TTY when standard input is a
	// TTY), force (always request a TTY) or auto (request a TTY
	// when opening a login session).  This option mirrors the
	// -t and -T flags for ssh(1).
	RequestTTY options.RequestTTYOption

	// Specifies the minimum RSA key size (in bits) that ssh(1)
	// will accept.  User authentication keys smaller than this
	// limit will be ignored.  Servers that present host keys
	// smaller than this limit will cause the connection to be
	// terminated.  The default is 1024 bits.  Note that this
	// limit may only be raised from the default.
	RequiredRSASize *int

	// Specifies revoked host public keys.  Keys listed in this
	// file will be refused for host authentication.  Note that
	// if this file does not exist or is not readable, then host
	// authentication will be refused for all hosts.  Keys may
	// be specified as a text file, listing one public key per
	// line, or as an OpenSSH Key Revocation List (KRL) as
	// generated by ssh-keygen(1).  For more information on
	// KRLs, see the KEY REVOCATION LISTS section in
	// ssh-keygen(1).  Arguments to RevokedHostKeys may use the
	// tilde syntax to refer to a user's home directory, the
	// tokens described in the "TOKENS" section and environment
	// variables as described in the "ENVIRONMENT VARIABLES"
	// section.
	RevokedHostKeys string // path

	// Specifies a path to a library that will be used when
	// loading any FIDO authenticator-hosted keys, overriding
	// the default of using the built-in USB HID support.
	//
	// If the specified value begins with a `$' character, then
	// it will be treated as an environment variable containing
	// the path to the library.
	SecurityKeyProvider string // path or env

	// Specifies what variables from the local environ(7) should
	// be sent to the server.  The server must also support it,
	// and the server must be configured to accept these
	// environment variables.  Note that the TERM environment
	// variable is always sent whenever a pseudo-terminal is
	// requested as it is required by the protocol.  Refer to
	// AcceptEnv in sshd_config(5) for how to configure the
	// server.  Variables are specified by name, which may
	// contain wildcard characters.  Multiple environment
	// variables may be separated by whitespace or spread across
	// multiple SendEnv directives.
	//
	// See "PATTERNS" for more information on patterns.
	//
	// It is possible to clear previously set SendEnv variable
	// names by prefixing patterns with -.  The default is not
	// to send any environment variables.
	//
	// NOTE: It is quite usual to have LANG and LC_* variables
	// in /etc/ssh/ssh_config, and since that file is read
	// last, using something like "SendEnv -*" in user config
	// or ssh options will not remove those.
	SendEnv []string // always append or use - prefix to remove.

	// Sets the number of server alive messages (see below)
	// which may be sent without ssh(1) receiving any messages
	// back from the server.  If this threshold is reached while
	// server alive messages are being sent, ssh will disconnect
	// from the server, terminating the session.  It is
	// important to note that the use of server alive messages
	// is very different from TCPKeepAlive (below).  The server
	// alive messages are sent through the encrypted channel and
	// therefore will not be spoofable.  The TCP keepalive
	// option enabled by TCPKeepAlive is spoofable.  The server
	// alive mechanism is valuable when the client or server
	// depend on knowing when a connection has become
	// unresponsive.
	//
	// The default value is 3.  If, for example,
	// ServerAliveInterval (see below) is set to 15 and
	// ServerAliveCountMax is left at the default, if the server
	// becomes unresponsive, ssh will disconnect after
	// approximately 45 seconds.
	ServerAliveCountMax *int

	// Sets a timeout interval in seconds after which if no data
	// has been received from the server, ssh(1) will send a
	// message through the encrypted channel to request a
	// response from the server.  The default is 0, indicating
	// that these messages will not be sent to the server.
	ServerAliveInterval time.Duration

	// May be used to either request invocation of a subsystem
	// on the remote system, or to prevent the execution of a
	// remote command at all.  The latter is useful for just
	// forwarding ports.  The argument to this keyword must be
	// none (same as the -N option), subsystem (same as the -s
	// option) or default (shell or command execution).
	SessionType string // enum

	// Directly specify one or more environment variables and
	// their contents to be sent to the server.  Similarly to
	// SendEnv, with the exception of the TERM variable, the
	// server must be prepared to accept the environment
	// variable.
	SetEnv map[string]string // always append

	// The SmartcardDevice parameter controls which smartcard device to use.
	SmartcardDevice string

	// Redirects stdin from /dev/null (actually, prevents
	// reading from stdin).  Either this or the equivalent -n
	// option must be used when ssh is run in the background.
	// The argument to this keyword must be yes (same as the -n
	// option) or no (the default).
	StdinNull options.BooleanOption

	// Sets the octal file creation mode mask (umask) used when
	// creating a Unix-domain socket file for local or remote
	// port forwarding.  This option is only used for port
	// forwarding to a Unix-domain socket file.
	//
	// The default value is 0177, which creates a Unix-domain
	// socket file that is readable and writable only by the
	// owner.  Note that not all operating systems honor the
	// file mode on Unix-domain socket files.
	StreamLocalBindMask *uint // should parse and output as octal

	// Specifies whether to remove an existing Unix-domain
	// socket file for local or remote port forwarding before
	// creating a new one.  If the socket file already exists
	// and StreamLocalBindUnlink is not enabled, ssh will be
	// unable to forward the port to the Unix-domain socket
	// file.  This option is only used for port forwarding to a
	// Unix-domain socket file.
	//
	// The argument must be yes or no (the default).
	StreamLocalBindUnlink options.BooleanOption

	// If this flag is set to yes, ssh(1) will never
	// automatically add host keys to the ~/.ssh/known_hosts
	// file, and refuses to connect to hosts whose host key has
	// changed.  This provides maximum protection against man-
	// in-the-middle (MITM) attacks, though it can be annoying
	// when the /etc/ssh/ssh_known_hosts file is poorly
	// maintained or when connections to new hosts are
	// frequently made.  This option forces the user to manually
	// add all new hosts.
	//
	// If this flag is set to accept-new then ssh will
	// automatically add new host keys to the user's known_hosts
	// file, but will not permit connections to hosts with
	// changed host keys.  If this flag is set to no or off, ssh
	// will automatically add new host keys to the user known
	// hosts files and allow connections to hosts with changed
	// hostkeys to proceed, subject to some restrictions.  If
	// this flag is set to ask (the default), new host keys will
	// be added to the user known host files only after the user
	// has confirmed that is what they really want to do, and
	// ssh will refuse to connect to hosts whose host key has
	// changed.  The host keys of known hosts will be verified
	// automatically in all cases.
	StrictHostKeyChecking options.StrictHostKeyCheckingOption

	// Gives the facility code that is used when logging
	// messages from ssh(1).  The possible values are: DAEMON,
	// USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4,
	// LOCAL5, LOCAL6, LOCAL7.  The default is USER.
	SyslogFacility string // use EnumSetter

	// Specifies whether the system should send TCP keepalive
	// messages to the other side.  If they are sent, death of
	// the connection or crash of one of the machines will be
	// properly noticed.  However, this means that connections
	// will die if the route is down temporarily, and some
	// people find it annoying.
	//
	// The default is yes (to send TCP keepalive messages), and
	// the client will notice if the network goes down or the
	// remote host dies.  This is important in scripts, and many
	// users want it too.
	//
	// To disable TCP keepalive messages, the value should be
	// set to no.  See also ServerAliveInterval for protocol-
	// level keepalives.
	TCPKeepAlive options.BooleanOption

	// Specify a configuration tag name that may be later used
	// by a Match directive to select a block of configuration.
	Tag string

	// Request tun(4) device forwarding between the client and
	// the server.  The argument must be yes, point-to-point
	// (layer 3), ethernet (layer 2), or no (the default).
	// Specifying yes requests the default tunnel mode, which is
	// point-to-point.
	Tunnel options.TunnelOption

	// Specifies the tun(4) devices to open on the client
	// (local_tun) and the server (remote_tun).
	//
	// The argument must be local_tun[:remote_tun].  The devices
	// may be specified by numerical ID or the keyword any,
	// which uses the next available tunnel device.  If
	// remote_tun is not specified, it defaults to any.  The
	// default is any:any.
	TunnelDevice string

	// Specifies whether ssh(1) should accept notifications of
	// additional hostkeys from the server sent after
	// authentication has completed and add them to
	// UserKnownHostsFile.  The argument must be yes, no or ask.
	// This option allows learning alternate hostkeys for a
	// server and supports graceful key rotation by allowing a
	// server to send replacement public keys before old ones
	// are removed.
	//
	// Additional hostkeys are only accepted if the key used to
	// authenticate the host was already trusted or explicitly
	// accepted by the user, the host was authenticated via
	// UserKnownHostsFile (i.e. not GlobalKnownHostsFile) and
	// the host was authenticated using a plain key and not a
	// certificate.
	//
	// UpdateHostKeys is enabled by default if the user has not
	// overridden the default UserKnownHostsFile setting and has
	// not enabled VerifyHostKeyDNS, otherwise UpdateHostKeys
	// will be set to no.
	//
	// If UpdateHostKeys is set to ask, then the user is asked
	// to confirm the modifications to the known_hosts file.
	// Confirmation is currently incompatible with
	// ControlPersist, and will be disabled if it is enabled.
	//
	// Presently, only sshd(8) from OpenSSH 6.8 and greater
	// support the "hostkeys@openssh.com" protocol extension
	// used to inform the client of all the server's hostkeys.
	UpdateHostKeys options.UpdateHostKeysOption

	// Specifies one or more files to use for the user host key
	// database, separated by whitespace.  Each filename may use
	// tilde notation to refer to the user's home directory, the
	// tokens described in the "TOKENS" section and environment
	// variables as described in the "ENVIRONMENT VARIABLES"
	// section.  A value of none causes ssh(1) to ignore any
	// user-specific known hosts files.  The default is
	// ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
	UserKnownHostsFile []string // none is special

	// Specifies whether to verify the remote key using DNS and
	// SSHFP resource records.  If this option is set to yes,
	// the client will implicitly trust keys that match a secure
	// fingerprint from DNS.  Insecure fingerprints will be
	// handled as if this option was set to ask.  If this option
	// is set to ask, information on fingerprint match will be
	// displayed, but the user will still need to confirm new
	// host keys according to the StrictHostKeyChecking option.
	// The default is no.
	//
	// See also "VERIFYING HOST KEYS" in ssh(1).
	VerifyHostKeyDNS options.VerifyHostKeyDNSOption

	// If this flag is set to yes, an ASCII art representation
	// of the remote host key fingerprint is printed in addition
	// to the fingerprint string at login and for unknown host
	// keys.  If this flag is set to no (the default), no
	// fingerprint strings are printed at login and only the
	// fingerprint string will be printed for unknown host keys.
	VisualHostKey options.BooleanOption

	// Specifies the full pathname of the xauth(1) program.  The
	// default is /usr/X11R6/bin/xauth.
	XAuthLocation string // path
}

Config contains every keyword known to exist in the ssh_config specification. The comments are taken from the manual page for ssh_config(5) and are used to describe the purpose of each keyword.

Please note that rig itself only supports a very limited subset of these settings.

func ConfigFor 

func ConfigFor(host string, opts ...ParserOption) (*Config, error)

ConfigFor returns a new Config for the given host.

This is a shorthand for creating a Parser, and using it to populate a Config object.

Do not use this if you need to get configurations for multiple hosts.

type Parser 

type Parser struct {
	// contains filtered or unexported fields
}

Parser for OpenSSH ssh_config files.

func NewParser 

func NewParser(r io.Reader, opts ...ParserOption) (*Parser, error)

NewParser returns a new Parser. If r is nil, the default ssh config files will be read from ~/.ssh/config and /etc/ssh/ssh_config (or %PROGRAMDATA%/ssh/ssh_config on Windows).

Calling NewParser will perform the initial parsing of the configuration files and returns an error if it fails.

If your use-case is to parse the configuration for multiple hosts, you only need to create one parser and use it to apply settings to multiple host objects by calling Apply multiple times with different objects..

func (*Parser) Apply 

func (p *Parser) Apply(obj any, host string) error

Apply the ssh config into the passed in object, such as an instance of Config. The object needs at least a Host (string) field.

func (*Parser) Reset 

func (p *Parser) Reset()

Reset resets the parser to its initial state.

type ParserOption 

type ParserOption func(*parserOptions)

ParserOption is a function that sets a parser option.

func WithExecutor 

func WithExecutor(e executor) ParserOption

WithExecutor is a functional option that overrides the default executor for testing (or disabling?) purposes.

func WithGlobalConfigPath 

func WithGlobalConfigPath(path string) ParserOption

WithGlobalConfigPath is a functional option that overrides the default global config path (/etc/ssh/ssh_config or %PROGRAMDATA%/ssh/ssh_config on Windows).

func WithGlobalConfigReader 

func WithGlobalConfigReader(r io.Reader) ParserOption

WithGlobalConfigReader is a functional option that overrides the default global config reader.

func WithNoFinalize 

func WithNoFinalize() ParserOption

WithNoFinalize is a functional option that disables the finalization of the object.

func WithStrict 

func WithStrict() ParserOption

WithStrict is a functional option that makes the parser respect the 'IgnoreUnknown' directive, thus making it error out on any encountered key that is not found and is not listed in the "IgnoreUnknown" config field.

func WithUserConfigPath 

func WithUserConfigPath(path string) ParserOption

WithUserConfigPath is a functional option that overrides the default user config path (~/.ssh/config).

func WithUserConfigReader 

func WithUserConfigReader(r io.Reader) ParserOption

WithUserConfigReader is a functional option that overrides the default user config reader.

func WithUserHome 

func WithUserHome(home string) ParserOption

WithUserHome is a functional option that sets the home directory for the current user.

type Setter 

type Setter struct {

	// The original host alias before any hostname canonicalization has been applied.
	OriginalHost string
	// When true, unknown fields will cause an error unless they match patterns defined in the IgnoreUnknown field.
	ErrorOnUnknownFields bool
	// contains filtered or unexported fields
}

Setter is a reflect based Setter for ssh configuration struct fields.

func NewSetter 

func NewSetter(obj any) (*Setter, error)

NewSetter creates a ssh config value setter for the given object. It can be used to set values on the object's fields using the same rules as the openssh client configuration parser via the Set(key, values...) function.

It is used internally by the Parser but it can be used to set values manually.

Example 
package main

import (
	"fmt"
	"log"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	type MyConfig struct {
		Host string
		Port int
	}
	obj := &MyConfig{}
	setter, err := sshconfig.NewSetter(obj)
	if err != nil {
		log.Fatal(err)
	}
	err = setter.Set("Host", "example.com")
	if err != nil {
		log.Fatal(err)
	}
	_ = setter.Set("Port", "2022")
	// On most of the config keys the first value to be set will remain in effect.
	_ = setter.Set("Port", "22")
	fmt.Println("Host:", obj.Host)
	fmt.Println("Port:", obj.Port)
}

Output:

Host: example.com
Port: 2022

func (*Setter) CanonicalizeHostname 

func (s *Setter) CanonicalizeHostname() error

CanonicalizeHostname performs hostname canonicalization. This is done automatically during the finalization phase when using parser.Apply.

It returns an error if the hostname couldn't be canonicalized and CanonicalizeFallbackLocal is not enabled, in which case you should not proceed with the connection.

func (*Setter) ExpandSlice 

func (s *Setter) ExpandSlice(key string) ([]string, error)

ExpandSlice expands any environment variables, tokens or tilde paths in the values. This is done automatically during the finalization phase, which can be disabled using the parser options.

func (*Setter) ExpandString 

func (s *Setter) ExpandString(key string) (string, error)

ExpandString expands any environment variables, tokens or tilde paths in the value. This is done automatically during the finalization phase, which can be disabled using the parser options.

func (*Setter) Finalize 

func (s *Setter) Finalize() error

Finalize goes through all the string slice fields and sets them to nil if they contain a single none value. It expands any tokens, environment variables or tilde-prefixed paths in the values for the keys where expansion is supported.

func (*Setter) HostChanged 

func (s *Setter) HostChanged() bool

HostChanged returns true if the value of "Host" (the host alias initially used to connect) has been changed. This happens if hostname canonicalization is performed. When connecting to the target, you should first check if Hostname is defined, if not, use the Host value.

func (*Setter) Reset 

func (s *Setter) Reset(key string) error

Reset sets a field to its zero value. This is useful in testing.

func (*Setter) Set 

func (s *Setter) Set(key string, values ...string) error

Set a value for a field by key name using the precedence rules of the SSH configuration file syntax.

Note that some of the fields take their values as separate strings and some as a comma-separated list, most only accept a single value.

Example 
package main

import (
	"fmt"
	"log"

	"github.com/k0sproject/rig/v2/sshconfig"
)

func main() {
	type MyConfig struct {
		Port int
	}
	obj := &MyConfig{}
	setter, err := sshconfig.NewSetter(obj)
	if err != nil {
		log.Fatal(err)
	}
	_ = setter.Set("Port", "2022")
	fmt.Println("Port:", obj.Port)
}

Output:

Port: 2022

Source Files

View all Source files

Directories

Path Synopsis
Package options defines a number of types that represent options that can be set in the SSH configuration file.
 Package options defines a number of types that represent options that can be set in the SSH configuration file.

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