1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 // Package jws provides a partial implementation
6 // of JSON Web Signature encoding and decoding.
7 // It exists to support the [golang.org/x/oauth2] package.
8 //
9 // See RFC 7515.
10 //
11 // Deprecated: this package is not intended for public use and might be
12 // removed in the future. It exists for internal use only.
13 // Please switch to another JWS package or copy this package into your own
14 // source tree.
15 package jws // import "golang.org/x/oauth2/jws"
16 17 import (
18 "bytes"
19 "crypto"
20 "crypto/rand"
21 "crypto/rsa"
22 "crypto/sha256"
23 "encoding/base64"
24 "encoding/json"
25 "errors"
26 "fmt"
27 "strings"
28 "time"
29 )
30 31 // ClaimSet contains information about the JWT signature including the
32 // permissions being requested (scopes), the target of the token, the issuer,
33 // the time the token was issued, and the lifetime of the token.
34 type ClaimSet struct {
35 Iss string `json:"iss"` // email address of the client_id of the application making the access token request
36 Scope string `json:"scope,omitempty"` // space-delimited list of the permissions the application requests
37 Aud string `json:"aud"` // descriptor of the intended target of the assertion (Optional).
38 Exp int64 `json:"exp"` // the expiration time of the assertion (seconds since Unix epoch)
39 Iat int64 `json:"iat"` // the time the assertion was issued (seconds since Unix epoch)
40 Typ string `json:"typ,omitempty"` // token type (Optional).
41 42 // Email for which the application is requesting delegated access (Optional).
43 Sub string `json:"sub,omitempty"`
44 45 // The old name of Sub. Client keeps setting Prn to be
46 // complaint with legacy OAuth 2.0 providers. (Optional)
47 Prn string `json:"prn,omitempty"`
48 49 // See http://tools.ietf.org/html/draft-jones-json-web-token-10#section-4.3
50 // This array is marshalled using custom code (see (c *ClaimSet) encode()).
51 PrivateClaims map[string]any `json:"-"`
52 }
53 54 func (c *ClaimSet) encode() (string, error) {
55 // Reverting time back for machines whose time is not perfectly in sync.
56 // If client machine's time is in the future according
57 // to Google servers, an access token will not be issued.
58 now := time.Now().Add(-10 * time.Second)
59 if c.Iat == 0 {
60 c.Iat = now.Unix()
61 }
62 if c.Exp == 0 {
63 c.Exp = now.Add(time.Hour).Unix()
64 }
65 if c.Exp < c.Iat {
66 return "", fmt.Errorf("jws: invalid Exp = %v; must be later than Iat = %v", c.Exp, c.Iat)
67 }
68 69 b, err := json.Marshal(c)
70 if err != nil {
71 return "", err
72 }
73 74 if len(c.PrivateClaims) == 0 {
75 return base64.RawURLEncoding.EncodeToString(b), nil
76 }
77 78 // Marshal private claim set and then append it to b.
79 prv, err := json.Marshal(c.PrivateClaims)
80 if err != nil {
81 return "", fmt.Errorf("jws: invalid map of private claims %v", c.PrivateClaims)
82 }
83 84 // Concatenate public and private claim JSON objects.
85 if !bytes.HasSuffix(b, []byte{'}'}) {
86 return "", fmt.Errorf("jws: invalid JSON %s", b)
87 }
88 if !bytes.HasPrefix(prv, []byte{'{'}) {
89 return "", fmt.Errorf("jws: invalid JSON %s", prv)
90 }
91 b[len(b)-1] = ',' // Replace closing curly brace with a comma.
92 b = append(b, prv[1:]...) // Append private claims.
93 return base64.RawURLEncoding.EncodeToString(b), nil
94 }
95 96 // Header represents the header for the signed JWS payloads.
97 type Header struct {
98 // The algorithm used for signature.
99 Algorithm string `json:"alg"`
100 101 // Represents the token type.
102 Typ string `json:"typ"`
103 104 // The optional hint of which key is being used.
105 KeyID string `json:"kid,omitempty"`
106 }
107 108 func (h *Header) encode() (string, error) {
109 b, err := json.Marshal(h)
110 if err != nil {
111 return "", err
112 }
113 return base64.RawURLEncoding.EncodeToString(b), nil
114 }
115 116 // Decode decodes a claim set from a JWS payload.
117 func Decode(payload string) (*ClaimSet, error) {
118 // decode returned id token to get expiry
119 _, claims, _, ok := parseToken(payload)
120 if !ok {
121 // TODO(jbd): Provide more context about the error.
122 return nil, errors.New("jws: invalid token received")
123 }
124 decoded, err := base64.RawURLEncoding.DecodeString(claims)
125 if err != nil {
126 return nil, err
127 }
128 c := &ClaimSet{}
129 err = json.NewDecoder(bytes.NewBuffer(decoded)).Decode(c)
130 return c, err
131 }
132 133 // Signer returns a signature for the given data.
134 type Signer func(data []byte) (sig []byte, err error)
135 136 // EncodeWithSigner encodes a header and claim set with the provided signer.
137 func EncodeWithSigner(header *Header, c *ClaimSet, sg Signer) (string, error) {
138 head, err := header.encode()
139 if err != nil {
140 return "", err
141 }
142 cs, err := c.encode()
143 if err != nil {
144 return "", err
145 }
146 ss := fmt.Sprintf("%s.%s", head, cs)
147 sig, err := sg([]byte(ss))
148 if err != nil {
149 return "", err
150 }
151 return fmt.Sprintf("%s.%s", ss, base64.RawURLEncoding.EncodeToString(sig)), nil
152 }
153 154 // Encode encodes a signed JWS with provided header and claim set.
155 // This invokes [EncodeWithSigner] using [crypto/rsa.SignPKCS1v15] with the given RSA private key.
156 func Encode(header *Header, c *ClaimSet, key *rsa.PrivateKey) (string, error) {
157 sg := func(data []byte) (sig []byte, err error) {
158 h := sha256.New()
159 h.Write(data)
160 return rsa.SignPKCS1v15(rand.Reader, key, crypto.SHA256, h.Sum(nil))
161 }
162 return EncodeWithSigner(header, c, sg)
163 }
164 165 // Verify tests whether the provided JWT token's signature was produced by the private key
166 // associated with the supplied public key.
167 func Verify(token string, key *rsa.PublicKey) error {
168 header, claims, sig, ok := parseToken(token)
169 if !ok {
170 return errors.New("jws: invalid token received, token must have 3 parts")
171 }
172 signatureString, err := base64.RawURLEncoding.DecodeString(sig)
173 if err != nil {
174 return err
175 }
176 177 h := sha256.New()
178 h.Write([]byte(header + tokenDelim + claims))
179 return rsa.VerifyPKCS1v15(key, crypto.SHA256, h.Sum(nil), signatureString)
180 }
181 182 func parseToken(s string) (header, claims, sig string, ok bool) {
183 header, s, ok = strings.Cut(s, tokenDelim)
184 if !ok { // no period found
185 return "", "", "", false
186 }
187 claims, s, ok = strings.Cut(s, tokenDelim)
188 if !ok { // only one period found
189 return "", "", "", false
190 }
191 sig, _, ok = strings.Cut(s, tokenDelim)
192 if ok { // three periods found
193 return "", "", "", false
194 }
195 return header, claims, sig, true
196 }
197 198 const tokenDelim = "."
199