Revokes the Access Token by accessing the De-authorization Endpoint
        of Health Graph API.
        
        @param access_token: Access Token for querying Health Graph API.

def revoke_access_token(self, access_token):
        """Revokes the Access Token by accessing the De-authorization Endpoint
        of Health Graph API.
        
        @param access_token: Access Token for querying Health Graph API.
        
        """
        payload = {'access_token': access_token,}
        req = requests.post(settings.API_DEAUTHORIZATION_URL, data=payload)