code: def validate_metadata_token(self, claims, endpoint):
          
          self._grant_types.extend(endpoint._grant_types.keys())
          claims.setdefault("token_endpoint_auth_methods_supported", ["client_secret_post", "client_secret_basic"])
  
          self.validate_metadata(claims, "token_endpoint_auth_methods_supported", is_list=True)
          self.validate_metadata(claims, "token_endpoint_auth_signing_alg_values_supported", is_list=True)
          self.validate_metadata(claims, "token_endpoint", is_required=True, is_url=True)
docs: If the token endpoint is used in the grant type, the value of this
          parameter MUST be the same as the value of the "grant_type"
          parameter passed to the token endpoint defined in the grant type
          definition.