Add public TokenRefresher

oauth2.go

@@ -260,6 +260,37 @@ func (c *Config) TokenSource(ctx context.Context, t *Token) TokenSource {
 	}
 }
 
+// TokenRefresher is a TokenSource that makes "grant_type"=="refresh_token"
+// HTTP requests to renew a token using a RefreshToken.
+type TokenRefresher struct {
+	ctx          context.Context // used to get HTTP requests
+	conf         *Config
+	refreshToken string
+}
+
+// WARNING: Token is not safe for concurrent access, as it
+// updates the tokenRefresher's refreshToken field.
+// Within this package, it is used by reuseTokenSource which
+// synchronizes calls to this method with its own mutex.
+func (tf *TokenRefresher) Token() (*Token, error) {
+	if tf.refreshToken == "" {
+		return nil, errors.New("oauth2: token expired and refresh token is not set")
+	}
+
+	tk, err := retrieveToken(tf.ctx, tf.conf, url.Values{
+		"grant_type":    {"refresh_token"},
+		"refresh_token": {tf.refreshToken},
+	})
+
+	if err != nil {
+		return nil, err
+	}
+	if tf.refreshToken != tk.RefreshToken {
+		tf.refreshToken = tk.RefreshToken
+	}
+	return tk, err
+}
+
 // tokenRefresher is a TokenSource that makes "grant_type"=="refresh_token"
 // HTTP requests to renew a token using a RefreshToken.
 type tokenRefresher struct {