docs: def _gssapi_login(self):
          """
          Authenticate to the /ssllogin endpoint with GSSAPI authentication.
  
          :returns: deferred that when fired returns a dict from sslLogin
          """
          method = treq_kerberos.post
          auth = treq_kerberos.TreqKerberosAuth(force_preemptive=True)
          return self._request_login(method, auth=auth)