def __call__(self, r):
if not is_secure_transport(r.url):<EOL><INDENT>raise InsecureTransportError()<EOL><DEDENT>r.url, r.headers, r.body = self._client.add_token(<EOL>r.url, http_method=r.method, body=r.body, headers=r.headers<EOL>)<EOL>return r<EOL>
Append an OAuth 2 token to the request.

        Note that currently HTTPS is required for all requests. There may be
        a token type that allows for plain HTTP in the future and then this
        should be updated to allow plain HTTP on a white list basis.