Returns Access Token retrieved from the Health Graph API Token 
        Endpoint following the login to RunKeeper.
        to RunKeeper. 
        
        @param code: Code returned by Health Graph API at the Authorization or
                     RunKeeper Login phase.
        @return:     Access Token for querying the Health Graph API.

def get_access_token(self, code):
        """Returns Access Token retrieved from the Health Graph API Token 
        Endpoint following the login to RunKeeper.
        to RunKeeper. 
        
        @param code: Code returned by Health Graph API at the Authorization or
                     RunKeeper Login phase.
        @return:     Access Token for querying the Health Graph API.
        
        """
        payload = {'grant_type': 'authorization_code',
                   'code': code,
                   'client_id': self._client_id,
                   'client_secret': self._client_secret,
                   'redirect_uri': self._redirect_uri,}
        req = requests.post(settings.API_ACCESS_TOKEN_URL, data=payload)
        data = req.json()
        return data.get('access_token')