def clientgetter(self, f):
self._clientgetter = f<EOL>return f<EOL>
Register a function as the client getter.

        The function accepts one parameter `client_key`, and it returns
        a client object with at least these information:

            - client_key: A random string
            - client_secret: A random string
            - redirect_uris: A list of redirect uris
            - default_realms: Default scopes of the client

        The client may contain more information, which is suggested:

            - default_redirect_uri: One of the redirect uris

        Implement the client getter::

            @oauth.clientgetter
            def get_client(client_key):
                client = get_client_model(client_key)
                # Client is an object
                return client