@Override
 public String toString() {
   return String.format(
       "OAuth context [\n"
           + "   OAuth service: %s\n"
           + "   state: %s\n"
           + "   authorization code: %s\n"
           + "   access token: %s\n"
           + "   refreshToken: %s\n"
           + "   expires in: %s\n",
       service.getClass().getName(),
       state,
       authorizationCode,
       accessToken,
       refreshToken,
       tokenExpirationDate);
 }