Accept a GSS-API context (server mode).

        :param str hostname: The servers hostname
        :param str username: The name of the user who attempts to login
        :param str recv_token: The GSS-API Token received from the server,
                               if it's not the initial call.
        :return: A ``String`` if the GSS-API has returned a token or ``None``
                if no token was returned

def ssh_accept_sec_context(self, hostname, recv_token, username=None):
        """
        Accept a GSS-API context (server mode).

        :param str hostname: The servers hostname
        :param str username: The name of the user who attempts to login
        :param str recv_token: The GSS-API Token received from the server,
                               if it's not the initial call.
        :return: A ``String`` if the GSS-API has returned a token or ``None``
                if no token was returned
        """
        # hostname and username are not required for GSSAPI, but for SSPI
        self._gss_host = hostname
        self._username = username
        if self._gss_srv_ctxt is None:
            self._gss_srv_ctxt = gssapi.AcceptContext()
        token = self._gss_srv_ctxt.step(recv_token)
        self._gss_srv_ctxt_status = self._gss_srv_ctxt.established
        return token