code: protected void doLogin(LoginCredential credential, LoginSpecifiedOption option) throws LoginFailureException {
          handleLoginSuccess(findLoginUser(credential).orElseThrow(() -> {
              final String msg = "Not found the user by the credential: " + credential + ", " + option;
              return handleLoginFailure(msg, credential, OptionalThing.of(option));
          }), option);
      }
docs: Do actually login for the user by credential.
  @param credential The login credential for the login user. (NotNull)
  @param option The option of login specified by caller. (NotNull)
  @throws LoginFailureException When it fails to do login by the user info.