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 RSA256 and HMAC SHA256, 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"])
	})

	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)

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.

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 ParseRSAPrivateKeyFromPEM(key []byte) (*rsa.PrivateKey, error)
• func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error)
• func RegisterSigningMethod(alg string, f func() SigningMethod)
• type Keyfunc
• type SigningMethod
  • func GetSigningMethod(alg string) (method SigningMethod)
• 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 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 (
	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 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 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 SigningMethod

type SigningMethod interface {
	Verify(signingString, signature string, key interface{}) error
	Sign(signingString string, key interface{}) (string, error)
	Alg() string
}

Signing method

func GetSigningMethod

func GetSigningMethod(alg string) (method SigningMethod)

Get a signing method from an "alg" string

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

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 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