jwt

README

A go (or 'golang' for search engine friendliness) implementation of JSON Web Tokens

NOTICE: A vulnerability in JWT was recently published. As this library doesn't force users to validate the alg is what they expected, it's possible your usage is effected. There will be an update soon to remedy this, and it will likey require backwards-incompatible changes to the API. In the short term, please make sure your implementation verifies the alg is what you expect.

What the heck is a JWT?

In short, it's a signed JSON object that does something useful (for example, authentication). It's commonly used for Bearer tokens in Oauth 2. A token is made of three parts, separated by .'s. The first two parts are JSON objects, that have been base64url encoded. The last part is the signature, encoded the same way.

The first part is called the header. It contains the necessary information for verifying the last part, the signature. For example, which encryption method was used for signing and what key was used.

The part in the middle is the interesting bit. It's called the Claims and contains the actual stuff you care about. Refer to the RFC for information about reserved keys and the proper way to add your own.

What's in the box?

This library supports the parsing and verification as well as the generation and signing of JWTs. Current supported signing algorithms are HMAC SHA, RSA, RSA-PSS, and ECDSA, though hooks are present for adding your own.

Parse and Verify

Parsing and verifying tokens is pretty straight forward. You pass in the token and a function for looking up the key. This is done as a callback since you may need to parse the token to find out what signing method and key was used.

	token, err := jwt.Parse(myToken, func(token *jwt.Token) (interface{}, error) {
		// Don't forget to validate the alg is what you expect:
		if _, ok := token.Method.(*jwt.SigningMethodRSA); !ok {
			return nil, fmt.Errorf("Unexpected signing method: %v", token.Header["alg"])
		}
		return myLookupKey(token.Header["kid"]), nil
	})

	if err == nil && token.Valid {
		deliverGoodness("!")
	} else {
		deliverUtterRejection(":(")
	}

Create a token

	// Create the token
	token := jwt.New(jwt.SigningMethodHS256)
	// Set some claims
	token.Claims["foo"] = "bar"
	token.Claims["exp"] = time.Now().Add(time.Hour * 72).Unix()
	// Sign and get the complete encoded token as a string
	tokenString, err := token.SignedString(mySigningKey)

Extensions

This library publishes all the necessary components for adding your own signing methods. Simply implement the SigningMethod interface and register a factory method using RegisterSigningMethod.

Here's an example of an extension that integrates with the Google App Engine signing tools: https://github.com/someone1/gcp-jwt-go

Project Status & Versioning

This library is considered production ready. Feedback and feature requests are appreciated. The API should be considered stable. There should be very few backwards-incompatible changes outside of major version updates (and only with good reason).

This project uses Semantic Versioning 2.0.0. Accepted pull requests will land on master. Periodically, versions will be tagged from master. You can find all the releases on the project releases page.

While we try to make it obvious when we make breaking changes, there isn't a great mechanism for pushing announcements out to users. You may want to use this alternative package include: gopkg.in/dgrijalva/jwt-go.v2. It will do the right thing WRT semantic versioning.

Usage Tips

Signing vs Encryption

A token is simply a JSON object that is signed by its author. this tells you exactly two things about the data:

• The author of the token was in the possession of the signing secret
• The data has not been modified since it was signed

It's important to know that JWT does not provide encryption, which means anyone who has access to the token can read its contents. If you need to protect (encrypt) the data, there is a companion spec, JWE, that provides this functionality. JWE is currently outside the scope of this library.

Choosing a Signing Method

There are several signing methods available, and you should probably take the time to learn about the various options before choosing one. The principal design decision is most likely going to be symmetric vs asymmetric.

Symmetric signing methods, such as HSA, use only a single secret. This is probably the simplest signing method to use since any []byte can be used as a valid secret. They are also slightly computationally faster to use, though this rarely is enough to matter. Symmetric signing methods work the best when both producers and consumers of tokens are trusted, or even the same system. Since the same secret is used to both sign and validate tokens, you can't easily distribute the key for validation.

Asymmetric signing methods, such as RSA, use different keys for signing and verifying tokens. This makes it possible to produce tokens with a private key, and allow any consumer to access the public key for verification.

JWT and OAuth

It's worth mentioning that OAuth and JWT are not the same thing. A JWT token is simply a signed JSON object. It can be used anywhere such a thing is useful. There is some confusion, though, as JWT is the most common type of bearer token used in OAuth2 authentication.

Without going too far down the rabbit hole, here's a description of the interaction of these technologies:

• OAuth is a protocol for allowing an identity provider to be separate from the service a user is logging in to. For example, whenever you use Facebook to log into a different service (Yelp, Spotify, etc), you are using OAuth.
• OAuth defines several options for passing around authentication data. One popular method is called a "bearer token". A bearer token is simply a string that should only be held by an authenticated user. Thus, simply presenting this token proves your identity. You can probably derive from here why a JWT might make a good bearer token.
• Because bearer tokens are used for authentication, it's important they're kept secret. This is why transactions that use bearer tokens typically happen over SSL.

More

Documentation can be found on godoc.org.

The command line utility included in this project (cmd/jwt) provides a straightforward example of token creation and parsing as well as a useful tool for debugging your own integration. For a more http centric example, see this gist.

Documentation

Overview

Package jwt is a Go implementation of JSON Web Tokens: http://self-issued.info/docs/draft-jones-json-web-token.html

See README.md for more info.

Index

• Constants
• Variables
• func DecodeSegment(seg string) ([]byte, error)
• func EncodeSegment(seg []byte) string
• func ParseECPrivateKeyFromPEM(key []byte) (*ecdsa.PrivateKey, error)
• func ParseECPublicKeyFromPEM(key []byte) (*ecdsa.PublicKey, error)
• func ParseRSAPrivateKeyFromPEM(key []byte) (*rsa.PrivateKey, error)
• func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error)
• func RegisterSigningMethod(alg string, f func() SigningMethod)
• type Keyfunc
• type Parser
  • func (p *Parser) Parse(tokenString string, keyFunc Keyfunc) (*Token, error)
• type SigningMethod
  • func GetSigningMethod(alg string) (method SigningMethod)
• type SigningMethodECDSA
  • func (m *SigningMethodECDSA) Alg() string
  • func (m *SigningMethodECDSA) Sign(signingString string, key interface{}) (string, error)
  • func (m *SigningMethodECDSA) Verify(signingString, signature string, key interface{}) error
• type SigningMethodHMAC
  • func (m *SigningMethodHMAC) Alg() string
  • func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string, error)
  • func (m *SigningMethodHMAC) Verify(signingString, signature string, key interface{}) error
• type SigningMethodRSA
  • func (m *SigningMethodRSA) Alg() string
  • func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string, error)
  • func (m *SigningMethodRSA) Verify(signingString, signature string, key interface{}) error
• type SigningMethodRSAPSS
  • func (m *SigningMethodRSAPSS) Sign(signingString string, key interface{}) (string, error)
  • func (m *SigningMethodRSAPSS) Verify(signingString, signature string, key interface{}) error
• type Token
  • func New(method SigningMethod) *Token
  • func Parse(tokenString string, keyFunc Keyfunc) (*Token, error)
  • func ParseFromRequest(req *http.Request, keyFunc Keyfunc) (token *Token, err error)
  • func (t *Token) SignedString(key interface{}) (string, error)
  • func (t *Token) SigningString() (string, error)
• type ValidationError
  • func (e ValidationError) Error() string

Constants

const (
	ValidationErrorMalformed        uint32 = 1 << iota // Token is malformed
	ValidationErrorUnverifiable                        // Token could not be verified because of signing problems
	ValidationErrorSignatureInvalid                    // Signature validation failed
	ValidationErrorExpired                             // Exp validation failed
	ValidationErrorNotValidYet                         // NBF validation failed
)

The errors that might occur when parsing and validating a token

Variables

var (
	ErrNotECPublicKey  = errors.New("Key is not a valid ECDSA public key")
	ErrNotECPrivateKey = errors.New("Key is not a valid ECDSA private key")
)

var (
	ErrInvalidKey       = errors.New("key is invalid or of invalid type")
	ErrHashUnavailable  = errors.New("the requested hash function is unavailable")
	ErrNoTokenInRequest = errors.New("no token present in request")
)

Error constants

var (
	ErrKeyMustBePEMEncoded = errors.New("Invalid Key: Key must be PEM encoded PKCS1 or PKCS8 private key")
	ErrNotRSAPrivateKey    = errors.New("Key is not a valid RSA private key")
)

var (
	// Sadly this is missing from crypto/ecdsa compared to crypto/rsa
	ErrECDSAVerification = errors.New("crypto/ecdsa: verification error")
)

var TimeFunc = time.Now

TimeFunc provides the current time when parsing token to validate "exp" claim (expiration time). You can override it to use another time value. This is useful for testing or if your server uses a different time zone than your tokens.

Functions

func DecodeSegment

func DecodeSegment(seg string) ([]byte, error)

Decode JWT specific base64url encoding with padding stripped

func EncodeSegment

func EncodeSegment(seg []byte) string

Encode JWT specific base64url encoding with padding stripped

func ParseECPrivateKeyFromPEM

func ParseECPrivateKeyFromPEM(key []byte) (*ecdsa.PrivateKey, error)

Parse PEM encoded Elliptic Curve Private Key Structure

func ParseECPublicKeyFromPEM

func ParseECPublicKeyFromPEM(key []byte) (*ecdsa.PublicKey, error)

Parse PEM encoded PKCS1 or PKCS8 public key

func ParseRSAPrivateKeyFromPEM

func ParseRSAPrivateKeyFromPEM(key []byte) (*rsa.PrivateKey, error)

Parse PEM encoded PKCS1 or PKCS8 private key

func ParseRSAPublicKeyFromPEM

func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error)

Parse PEM encoded PKCS1 or PKCS8 public key

func RegisterSigningMethod

func RegisterSigningMethod(alg string, f func() SigningMethod)

Register the "alg" name and a factory function for signing method. This is typically done during init() in the method's implementation

Types

type Keyfunc

type Keyfunc func(*Token) (interface{}, error)

Parse methods use this callback function to supply the key for verification. The function receives the parsed, but unverified Token. This allows you to use propries in the Header of the token (such as `kid`) to identify which key to use.

type Parser

type Parser struct {
	ValidMethods  []string // If populated, only these methods will be considered valid
	UseJSONNumber bool     // Use JSON Number format in JSON decoder
}

func (*Parser) Parse

func (p *Parser) Parse(tokenString string, keyFunc Keyfunc) (*Token, error)

Parse, validate, and return a token. keyFunc will receive the parsed token and should return the key for validating. If everything is kosher, err will be nil

type SigningMethod

type SigningMethod interface {
	Verify(signingString, signature string, key interface{}) error // Returns nil if signature is valid
	Sign(signingString string, key interface{}) (string, error)    // Returns encoded signature or error
	Alg() string                                                   // returns the alg identifier for this method (example: 'HS256')
}

Implement SigningMethod to add new methods for signing or verifying tokens.

func GetSigningMethod

func GetSigningMethod(alg string) (method SigningMethod)

Get a signing method from an "alg" string

type SigningMethodECDSA

type SigningMethodECDSA struct {
	Name      string
	Hash      crypto.Hash
	KeySize   int
	CurveBits int
}

Implements the ECDSA family of signing methods signing methods

var (
	SigningMethodES256 *SigningMethodECDSA
	SigningMethodES384 *SigningMethodECDSA
	SigningMethodES512 *SigningMethodECDSA
)

Specific instances for EC256 and company

func (*SigningMethodECDSA) Alg

func (m *SigningMethodECDSA) Alg() string

func (*SigningMethodECDSA) Sign

func (m *SigningMethodECDSA) Sign(signingString string, key interface{}) (string, error)

Implements the Sign method from SigningMethod For this signing method, key must be an ecdsa.PrivateKey struct

func (*SigningMethodECDSA) Verify

func (m *SigningMethodECDSA) Verify(signingString, signature string, key interface{}) error

Implements the Verify method from SigningMethod For this verify method, key must be an ecdsa.PublicKey struct

type SigningMethodHMAC

type SigningMethodHMAC struct {
	Name string
	Hash crypto.Hash
}

Implements the HMAC-SHA family of signing methods signing methods

var (
	SigningMethodHS256  *SigningMethodHMAC
	SigningMethodHS384  *SigningMethodHMAC
	SigningMethodHS512  *SigningMethodHMAC
	ErrSignatureInvalid = errors.New("signature is invalid")
)

Specific instances for HS256 and company

func (*SigningMethodHMAC) Alg

func (m *SigningMethodHMAC) Alg() string

func (*SigningMethodHMAC) Sign

func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string, error)

Implements the Sign method from SigningMethod for this signing method. Key must be []byte

func (*SigningMethodHMAC) Verify

func (m *SigningMethodHMAC) Verify(signingString, signature string, key interface{}) error

Verify the signature of HSXXX tokens. Returns nil if the signature is valid.

type SigningMethodRSA

type SigningMethodRSA struct {
	Name string
	Hash crypto.Hash
}

Implements the RSA family of signing methods signing methods

var (
	SigningMethodRS256 *SigningMethodRSA
	SigningMethodRS384 *SigningMethodRSA
	SigningMethodRS512 *SigningMethodRSA
)

Specific instances for RS256 and company

func (*SigningMethodRSA) Alg

func (m *SigningMethodRSA) Alg() string

func (*SigningMethodRSA) Sign

func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string, error)

Implements the Sign method from SigningMethod For this signing method, must be either a PEM encoded PKCS1 or PKCS8 RSA private key as []byte, or an rsa.PrivateKey structure.

func (*SigningMethodRSA) Verify

func (m *SigningMethodRSA) Verify(signingString, signature string, key interface{}) error

Implements the Verify method from SigningMethod For this signing method, must be either a PEM encoded PKCS1 or PKCS8 RSA public key as []byte, or an rsa.PublicKey structure.

type SigningMethodRSAPSS

type SigningMethodRSAPSS struct {
	*SigningMethodRSA
	Options *rsa.PSSOptions
}

Implements the RSAPSS family of signing methods signing methods

var (
	SigningMethodPS256 *SigningMethodRSAPSS
	SigningMethodPS384 *SigningMethodRSAPSS
	SigningMethodPS512 *SigningMethodRSAPSS
)

Specific instances for RS/PS and company

func (*SigningMethodRSAPSS) Sign

func (m *SigningMethodRSAPSS) Sign(signingString string, key interface{}) (string, error)

Implements the Sign method from SigningMethod For this signing method, key must be an rsa.PrivateKey struct

func (*SigningMethodRSAPSS) Verify

func (m *SigningMethodRSAPSS) Verify(signingString, signature string, key interface{}) error

Implements the Verify method from SigningMethod For this verify method, key must be an rsa.PublicKey struct

type Token

type Token struct {
	Raw       string                 // The raw token.  Populated when you Parse a token
	Method    SigningMethod          // The signing method used or to be used
	Header    map[string]interface{} // The first segment of the token
	Claims    map[string]interface{} // The second segment of the token
	Signature string                 // The third segment of the token.  Populated when you Parse a token
	Valid     bool                   // Is the token valid?  Populated when you Parse/Verify a token
}

A JWT Token. Different fields will be used depending on whether you're creating or parsing/verifying a token.

func New

func New(method SigningMethod) *Token

Create a new Token. Takes a signing method

func Parse

func Parse(tokenString string, keyFunc Keyfunc) (*Token, error)

Parse, validate, and return a token. keyFunc will receive the parsed token and should return the key for validating. If everything is kosher, err will be nil

func ParseFromRequest

func ParseFromRequest(req *http.Request, keyFunc Keyfunc) (token *Token, err error)

Try to find the token in an http.Request. This method will call ParseMultipartForm if there's no token in the header. Currently, it looks in the Authorization header as well as looking for an 'access_token' request parameter in req.Form.

func (*Token) SignedString

func (t *Token) SignedString(key interface{}) (string, error)

Get the complete, signed token

func (*Token) SigningString

func (t *Token) SigningString() (string, error)

Generate the signing string. This is the most expensive part of the whole deal. Unless you need this for something special, just go straight for the SignedString.

type ValidationError

type ValidationError struct {
	Errors uint32 // bitfield.  see ValidationError... constants
	// contains filtered or unexported fields
}

The error from Parse if token is not valid

func (ValidationError) Error

func (e ValidationError) Error() string

Validation error is an error type