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// Copyright 2014 The oauth2 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 (
"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
Iat int64 `json:"iat"` // the time the assertion was issued.
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:"-"`
exp time.Time
iat time.Time
}
func (c *ClaimSet) encode() (string, error) {
if c.exp.IsZero() || c.iat.IsZero() {
// 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)
c.iat = now
c.exp = now.Add(time.Hour)
}
c.Exp = c.exp.Unix()
c.Iat = c.iat.Unix()
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
}
// Encode encodes a signed JWS with provided header and claim set.
func Encode(header *Header, c *ClaimSet, signature *rsa.PrivateKey) (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)
h := sha256.New()
h.Write([]byte(ss))
b, err := rsa.SignPKCS1v15(rand.Reader, signature, crypto.SHA256, h.Sum(nil))
if err != nil {
return "", err
}
sig := base64Encode(b)
return fmt.Sprintf("%s.%s", ss, sig), nil
}
// 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 2:
s += "=="
case 3:
s += "="
}
return base64.URLEncoding.DecodeString(s)
}
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