// JWTAccessTokenSourceFromJSON uses a Google Developers service account JSON
// key file to read the credentials that authorize and authenticate the
// requests, and returns a TokenSource that does not use any OAuth2 flow but
// instead creates a JWT and sends that as the access token.
// The audience is typically a URL that specifies the scope of the credentials.
//
// Note that this is not a standard OAuth flow, but rather an
// optimization supported by a few Google services.
// Unless you know otherwise, you should use JWTConfigFromJSON instead.
func JWTAccessTokenSourceFromJSON(jsonKey []byte, audience string) (oauth2.TokenSource, error) {
cfg, err := JWTConfigFromJSON(jsonKey)
if err != nil {
return nil, fmt.Errorf("google: could not parse JSON key: %v", err)
}
pk, err := internal.ParseKey(cfg.PrivateKey)
if err != nil {
return nil, fmt.Errorf("google: could not parse key: %v", err)
}
ts := &jwtAccessTokenSource{
email: cfg.Email,
audience: audience,
pk: pk,
}
tok, err := ts.Token()
if err != nil {
return nil, err
}
return oauth2.ReuseTokenSource(tok, ts), nil
}
func (js jwtSource) Token() (*oauth2.Token, error) {
pk, err := internal.ParseKey(js.conf.PrivateKey)
if err != nil {
return nil, err
}
hc := oauth2.NewClient(js.ctx, nil)
claimSet := &jws.ClaimSet{
Iss: js.conf.Email,
Scope: strings.Join(js.conf.Scopes, " "),
Aud: js.conf.TokenURL,
}
if subject := js.conf.Subject; subject != "" {
claimSet.Sub = subject
// prn is the old name of sub. Keep setting it
// to be compatible with legacy OAuth 2.0 providers.
claimSet.Prn = subject
}
payload, err := jws.Encode(defaultHeader, claimSet, pk)
if err != nil {
return nil, err
}
v := url.Values{}
v.Set("grant_type", defaultGrantType)
v.Set("assertion", payload)
resp, err := hc.PostForm(js.conf.TokenURL, v)
if err != nil {
return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
}
if c := resp.StatusCode; c < 200 || c > 299 {
return nil, fmt.Errorf("oauth2: cannot fetch token: %v\nResponse: %s", resp.Status, body)
}
// tokenRes is the JSON response body.
var tokenRes struct {
AccessToken string `json:"access_token"`
TokenType string `json:"token_type"`
IDToken string `json:"id_token"`
ExpiresIn int64 `json:"expires_in"` // relative seconds from now
}
if err := json.Unmarshal(body, &tokenRes); err != nil {
return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
}
token := &oauth2.Token{
AccessToken: tokenRes.AccessToken,
TokenType: tokenRes.TokenType,
}
raw := make(map[string]interface{})
json.Unmarshal(body, &raw) // no error checks for optional fields
token = token.WithExtra(raw)
if secs := tokenRes.ExpiresIn; secs > 0 {
token.Expiry = time.Now().Add(time.Duration(secs) * time.Second)
}
if v := tokenRes.IDToken; v != "" {
// decode returned id token to get expiry
claimSet, err := jws.Decode(v)
if err != nil {
return nil, fmt.Errorf("oauth2: error decoding JWT token: %v", err)
}
token.Expiry = time.Unix(claimSet.Exp, 0)
}
return token, nil
}