'Refreshes the access_token.
Skip all the storage hoops and just refresh using the API.
Args:
http_request: callable, a callable that matches the method signature of
httplib2.Http.request, used to make the refresh request.
Raises:
AccessTokenRefreshError: When the refresh fails.'

def _refresh(self, http_request):

    uri = uritemplate.expand(META, {'scope': self.scope})
    (response, content) = http_request(uri)
    if (response.status == 200):
        try:
            d = simplejson.loads(content)
        except StandardError as e:
            raise AccessTokenRefreshError(str(e))
        self.access_token = d['accessToken']
    else:
        raise AccessTokenRefreshError(content)
