code: def _authn_context_decl_ref(decl_ref, authn_auth=None):
      
      return factory(saml.AuthnContext,
                     authn_context_decl_ref=decl_ref,
                     authenticating_authority=factory(
                         saml.AuthenticatingAuthority, text=authn_auth))
docs: Construct the authn context with a authn context declaration reference
      :param decl_ref: The authn context declaration reference
      :param authn_auth: Authenticating Authority
      :return: An AuthnContext instance