def validate_metadata_server(self):
        """
        Authorization servers can have metadata describing their
        configuration.  The following authorization server metadata values
        are used by this specification. More details can be found in
        `RFC8414 section 2`_ :

       issuer
          REQUIRED

       authorization_endpoint
          URL of the authorization server's authorization endpoint
          [`RFC6749#Authorization`_].  This is REQUIRED unless no grant types are supported
          that use the authorization endpoint.

       token_endpoint
          URL of the authorization server's token endpoint [`RFC6749#Token`_].  This
          is REQUIRED unless only the implicit grant type is supported.

       scopes_supported
          RECOMMENDED.

       response_types_supported
          REQUIRED.

       * Other OPTIONAL fields:
       jwks_uri
       registration_endpoint
       response_modes_supported

       grant_types_supported
          OPTIONAL.  JSON array containing a list of the OAuth 2.0 grant
          type values that this authorization server supports.  The array
          values used are the same as those used with the "grant_types"
          parameter defined by "OAuth 2.0 Dynamic Client Registration
          Protocol" [`RFC7591`_].  If omitted, the default value is
          "["authorization_code", "implicit"]".

       token_endpoint_auth_methods_supported

       token_endpoint_auth_signing_alg_values_supported

       service_documentation

       ui_locales_supported

       op_policy_uri

       op_tos_uri

       revocation_endpoint

       revocation_endpoint_auth_methods_supported

       revocation_endpoint_auth_signing_alg_values_supported

       introspection_endpoint

       introspection_endpoint_auth_methods_supported

       introspection_endpoint_auth_signing_alg_values_supported

       code_challenge_methods_supported

       Additional authorization server metadata parameters MAY also be used.
       Some are defined by other specifications, such as OpenID Connect
       Discovery 1.0 [`OpenID.Discovery`_].

        .. _`RFC8414 section 2`: https://tools.ietf.org/html/rfc8414#section-2
        .. _`RFC6749#Authorization`: https://tools.ietf.org/html/rfc6749#section-3.1
        .. _`RFC6749#Token`: https://tools.ietf.org/html/rfc6749#section-3.2
        .. _`RFC7591`: https://tools.ietf.org/html/rfc7591
        .. _`OpenID.Discovery`: https://openid.net/specs/openid-connect-discovery-1_0.html
        """
        claims = copy.deepcopy(self.initial_claims)
        self.validate_metadata(claims, "issuer", is_required=True, is_issuer=True)
        self.validate_metadata(claims, "jwks_uri", is_url=True)
        self.validate_metadata(claims, "scopes_supported", is_list=True)
        self.validate_metadata(claims, "service_documentation", is_url=True)
        self.validate_metadata(claims, "ui_locales_supported", is_list=True)
        self.validate_metadata(claims, "op_policy_uri", is_url=True)
        self.validate_metadata(claims, "op_tos_uri", is_url=True)

        self._grant_types = []
        for endpoint in self.endpoints:
            if isinstance(endpoint, TokenEndpoint):
                self.validate_metadata_token(claims, endpoint)
            if isinstance(endpoint, AuthorizationEndpoint):
                self.validate_metadata_authorization(claims, endpoint)
            if isinstance(endpoint, RevocationEndpoint):
                self.validate_metadata_revocation(claims, endpoint)
            if isinstance(endpoint, IntrospectEndpoint):
                self.validate_metadata_introspection(claims, endpoint)

        # "grant_types_supported" is a combination of all OAuth2 grant types
        # allowed in the current provider implementation.
        claims.setdefault("grant_types_supported", self._grant_types)
        self.validate_metadata(claims, "grant_types_supported", is_list=True)
        return claims
Authorization servers can have metadata describing their
        configuration.  The following authorization server metadata values
        are used by this specification. More details can be found in
        `RFC8414 section 2`_ :

       issuer
          REQUIRED

       authorization_endpoint
          URL of the authorization server's authorization endpoint
          [`RFC6749#Authorization`_].  This is REQUIRED unless no grant types are supported
          that use the authorization endpoint.

       token_endpoint
          URL of the authorization server's token endpoint [`RFC6749#Token`_].  This
          is REQUIRED unless only the implicit grant type is supported.

       scopes_supported
          RECOMMENDED.

       response_types_supported
          REQUIRED.

       * Other OPTIONAL fields:
       jwks_uri
       registration_endpoint
       response_modes_supported

       grant_types_supported
          OPTIONAL.  JSON array containing a list of the OAuth 2.0 grant
          type values that this authorization server supports.  The array
          values used are the same as those used with the "grant_types"
          parameter defined by "OAuth 2.0 Dynamic Client Registration
          Protocol" [`RFC7591`_].  If omitted, the default value is
          "["authorization_code", "implicit"]".

       token_endpoint_auth_methods_supported

       token_endpoint_auth_signing_alg_values_supported

       service_documentation

       ui_locales_supported

       op_policy_uri

       op_tos_uri

       revocation_endpoint

       revocation_endpoint_auth_methods_supported

       revocation_endpoint_auth_signing_alg_values_supported

       introspection_endpoint

       introspection_endpoint_auth_methods_supported

       introspection_endpoint_auth_signing_alg_values_supported

       code_challenge_methods_supported

       Additional authorization server metadata parameters MAY also be used.
       Some are defined by other specifications, such as OpenID Connect
       Discovery 1.0 [`OpenID.Discovery`_].

        .. _`RFC8414 section 2`: https://tools.ietf.org/html/rfc8414#section-2
        .. _`RFC6749#Authorization`: https://tools.ietf.org/html/rfc6749#section-3.1
        .. _`RFC6749#Token`: https://tools.ietf.org/html/rfc6749#section-3.2
        .. _`RFC7591`: https://tools.ietf.org/html/rfc7591
        .. _`OpenID.Discovery`: https://openid.net/specs/openid-connect-discovery-1_0.html