docs: def get_login_url(self, state=None):
          """Generates and returns URL for redirecting to Login Page of RunKeeper,
          which is the Authorization Endpoint of Health Graph API.
          
          @param state: State string. Passed to client web application at the end
                        of the Login Process.
          @return:      URL for redirecting to RunKeeper Login Page.  
          
          """
          payload = {'response_type': 'code',
                     'client_id': self._client_id,
                     'redirect_uri': self._redirect_uri,}
          if state is not None:
              payload['state'] = state
          return "%s?%s" % (settings.API_AUTHORIZATION_URL,
                            urllib.urlencode(payload))