def authorize_url(self, return_url, **kwargs):
return url_for('<STR_LIT>', return_url=return_url, **kwargs)<EOL>
Creates a URL that can be used to start the authorization flow.

        When the user is directed to the URL, the authorization flow will
        begin. Once complete, the user will be redirected to the specified
        return URL.

        Any kwargs are passed into the flow constructor.