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jwt.go
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jwt.go
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package jwt
import (
"encoding/base64"
"encoding/json"
"net/http"
"strings"
"time"
)
// 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.
var TimeFunc = time.Now
// 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 Keyfunc func(*Token) (interface{}, error)
// A JWT Token. Different fields will be used depending on whether you're
// creating or parsing/verifying a 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
}
// Create a new Token. Takes a signing method
func New(method SigningMethod) *Token {
return &Token{
Header: map[string]interface{}{
"typ": "JWT",
"alg": method.Alg(),
},
Claims: make(map[string]interface{}),
Method: method,
}
}
// Get the complete, signed token
func (t *Token) SignedString(key interface{}) (string, error) {
var sig, sstr string
var err error
if sstr, err = t.SigningString(); err != nil {
return "", err
}
if sig, err = t.Method.Sign(sstr, key); err != nil {
return "", err
}
return strings.Join([]string{sstr, sig}, "."), nil
}
// 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.
func (t *Token) SigningString() (string, error) {
var err error
parts := make([]string, 2)
for i, _ := range parts {
var source map[string]interface{}
if i == 0 {
source = t.Header
} else {
source = t.Claims
}
var jsonValue []byte
if jsonValue, err = json.Marshal(source); err != nil {
return "", err
}
parts[i] = EncodeSegment(jsonValue)
}
return strings.Join(parts, "."), nil
}
// 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 Parse(tokenString string, keyFunc Keyfunc) (*Token, error) {
parts := strings.Split(tokenString, ".")
if len(parts) != 3 {
return nil, &ValidationError{err: "token contains an invalid number of segments", Errors: ValidationErrorMalformed}
}
var err error
token := &Token{Raw: tokenString}
// parse Header
var headerBytes []byte
if headerBytes, err = DecodeSegment(parts[0]); err != nil {
return token, &ValidationError{err: err.Error(), Errors: ValidationErrorMalformed}
}
if err = json.Unmarshal(headerBytes, &token.Header); err != nil {
return token, &ValidationError{err: err.Error(), Errors: ValidationErrorMalformed}
}
// parse Claims
var claimBytes []byte
if claimBytes, err = DecodeSegment(parts[1]); err != nil {
return token, &ValidationError{err: err.Error(), Errors: ValidationErrorMalformed}
}
if err = json.Unmarshal(claimBytes, &token.Claims); err != nil {
return token, &ValidationError{err: err.Error(), Errors: ValidationErrorMalformed}
}
// Lookup signature method
if method, ok := token.Header["alg"].(string); ok {
if token.Method = GetSigningMethod(method); token.Method == nil {
return token, &ValidationError{err: "signing method (alg) is unavailable.", Errors: ValidationErrorUnverifiable}
}
} else {
return token, &ValidationError{err: "signing method (alg) is unspecified.", Errors: ValidationErrorUnverifiable}
}
// Lookup key
var key interface{}
if keyFunc == nil {
// keyFunc was not provided. short circuiting validation
return token, &ValidationError{err: "no Keyfunc was provided.", Errors: ValidationErrorUnverifiable}
}
if key, err = keyFunc(token); err != nil {
// keyFunc returned an error
return token, &ValidationError{err: err.Error(), Errors: ValidationErrorUnverifiable}
}
// Check expiration times
vErr := &ValidationError{}
now := TimeFunc().Unix()
if exp, ok := token.Claims["exp"].(float64); ok {
if now > int64(exp) {
vErr.err = "token is expired"
vErr.Errors |= ValidationErrorExpired
}
}
if nbf, ok := token.Claims["nbf"].(float64); ok {
if now < int64(nbf) {
vErr.err = "token is not valid yet"
vErr.Errors |= ValidationErrorNotValidYet
}
}
// Perform validation
if err = token.Method.Verify(strings.Join(parts[0:2], "."), parts[2], key); err != nil {
vErr.err = err.Error()
vErr.Errors |= ValidationErrorSignatureInvalid
}
if vErr.valid() {
token.Valid = true
return token, nil
}
return token, vErr
}
// 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 ParseFromRequest(req *http.Request, keyFunc Keyfunc) (token *Token, err error) {
// Look for an Authorization header
if ah := req.Header.Get("Authorization"); ah != "" {
// Should be a bearer token
if len(ah) > 6 && strings.ToUpper(ah[0:6]) == "BEARER" {
return Parse(ah[7:], keyFunc)
}
}
// Look for "access_token" parameter
req.ParseMultipartForm(10e6)
if tokStr := req.Form.Get("access_token"); tokStr != "" {
return Parse(tokStr, keyFunc)
}
return nil, ErrNoTokenInRequest
}
// Encode JWT specific base64url encoding with padding stripped
func EncodeSegment(seg []byte) string {
return strings.TrimRight(base64.URLEncoding.EncodeToString(seg), "=")
}
// Decode JWT specific base64url encoding with padding stripped
func DecodeSegment(seg string) ([]byte, error) {
if l := len(seg) % 4; l > 0 {
seg += strings.Repeat("=", 4-l)
}
return base64.URLEncoding.DecodeString(seg)
}