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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package jws provides encoding and decoding utilities for
// signed JWS messages.
package jws // import "golang.org/x/oauth2/jws"
import (
"bytes"
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"strings"
"time"
)
// ClaimSet contains information about the JWT signature including the
// permissions being requested (scopes), the target of the token, the issuer,
// the time the token was issued, and the lifetime of the token.
type ClaimSet struct {
Iss string `json:"iss"` // email address of the client_id of the application making the access token request
Scope string `json:"scope,omitempty"` // space-delimited list of the permissions the application requests
Aud string `json:"aud"` // descriptor of the intended target of the assertion (Optional).
Exp int64 `json:"exp"` // the expiration time of the assertion (seconds since Unix epoch)
Iat int64 `json:"iat"` // the time the assertion was issued (seconds since Unix epoch)
Typ string `json:"typ,omitempty"` // token type (Optional).
// Email for which the application is requesting delegated access (Optional).
Sub string `json:"sub,omitempty"`
// The old name of Sub. Client keeps setting Prn to be
// complaint with legacy OAuth 2.0 providers. (Optional)
Prn string `json:"prn,omitempty"`
// See http://tools.ietf.org/html/draft-jones-json-web-token-10#section-4.3
// This array is marshalled using custom code (see (c *ClaimSet) encode()).
PrivateClaims map[string]interface{} `json:"-"`
}
func (c *ClaimSet) encode() (string, error) {
// Reverting time back for machines whose time is not perfectly in sync.
// If client machine's time is in the future according
// to Google servers, an access token will not be issued.
now := time.Now().Add(-10 * time.Second)
if c.Iat == 0 {
c.Iat = now.Unix()
}
if c.Exp == 0 {
c.Exp = now.Add(time.Hour).Unix()
}
if c.Exp < c.Iat {
return "", fmt.Errorf("jws: invalid Exp = %v; must be later than Iat = %v", c.Exp, c.Iat)
}
b, err := json.Marshal(c)
if err != nil {
return "", err
}
if len(c.PrivateClaims) == 0 {
return base64Encode(b), nil
}
// Marshal private claim set and then append it to b.
prv, err := json.Marshal(c.PrivateClaims)
if err != nil {
return "", fmt.Errorf("jws: invalid map of private claims %v", c.PrivateClaims)
}
// Concatenate public and private claim JSON objects.
if !bytes.HasSuffix(b, []byte{'}'}) {
return "", fmt.Errorf("jws: invalid JSON %s", b)
}
if !bytes.HasPrefix(prv, []byte{'{'}) {
return "", fmt.Errorf("jws: invalid JSON %s", prv)
}
b[len(b)-1] = ',' // Replace closing curly brace with a comma.
b = append(b, prv[1:]...) // Append private claims.
return base64Encode(b), nil
}
// Header represents the header for the signed JWS payloads.
type Header struct {
// The algorithm used for signature.
Algorithm string `json:"alg"`
// Represents the token type.
Typ string `json:"typ"`
}
func (h *Header) encode() (string, error) {
b, err := json.Marshal(h)
if err != nil {
return "", err
}
return base64Encode(b), nil
}
// Decode decodes a claim set from a JWS payload.
func Decode(payload string) (*ClaimSet, error) {
// decode returned id token to get expiry
s := strings.Split(payload, ".")
if len(s) < 2 {
// TODO(jbd): Provide more context about the error.
return nil, errors.New("jws: invalid token received")
}
decoded, err := base64Decode(s[1])
if err != nil {
return nil, err
}
c := &ClaimSet{}
err = json.NewDecoder(bytes.NewBuffer(decoded)).Decode(c)
return c, err
}
// Signer returns a signature for the given data.
type Signer func(data []byte) (sig []byte, err error)
// EncodeWithSigner encodes a header and claim set with the provided signer.
func EncodeWithSigner(header *Header, c *ClaimSet, sg Signer) (string, error) {
head, err := header.encode()
if err != nil {
return "", err
}
cs, err := c.encode()
if err != nil {
return "", err
}
ss := fmt.Sprintf("%s.%s", head, cs)
sig, err := sg([]byte(ss))
if err != nil {
return "", err
}
return fmt.Sprintf("%s.%s", ss, base64Encode(sig)), nil
}
// Encode encodes a signed JWS with provided header and claim set.
// This invokes EncodeWithSigner using crypto/rsa.SignPKCS1v15 with the given RSA private key.
func Encode(header *Header, c *ClaimSet, key *rsa.PrivateKey) (string, error) {
sg := func(data []byte) (sig []byte, err error) {
h := sha256.New()
h.Write(data)
return rsa.SignPKCS1v15(rand.Reader, key, crypto.SHA256, h.Sum(nil))
}
return EncodeWithSigner(header, c, sg)
}
// Verify tests whether the provided JWT token's signature was produced by the private key
// associated with the supplied public key.
func Verify(token string, key *rsa.PublicKey) error {
parts := strings.Split(token, ".")
if len(parts) != 3 {
return errors.New("jws: invalid token received, token must have 3 parts")
}
signedContent := parts[0] + "." + parts[1]
signatureString, err := base64Decode(parts[2])
if err != nil {
return err
}
h := sha256.New()
h.Write([]byte(signedContent))
return rsa.VerifyPKCS1v15(key, crypto.SHA256, h.Sum(nil), []byte(signatureString))
}
// base64Encode returns and Base64url encoded version of the input string with any
// trailing "=" stripped.
func base64Encode(b []byte) string {
return strings.TrimRight(base64.URLEncoding.EncodeToString(b), "=")
}
// base64Decode decodes the Base64url encoded string
func base64Decode(s string) ([]byte, error) {
// add back missing padding
switch len(s) % 4 {
case 1:
s += "==="
case 2:
s += "=="
case 3:
s += "="
}
return base64.URLEncoding.DecodeString(s)
}
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