'Refreshes the access token.
Args:
http: unused HTTP object'

def _refresh(self, http):

    self.devshell_response = _SendRecv()
    self.access_token = self.devshell_response.access_token
    expires_in = self.devshell_response.expires_in
    if (expires_in is not None):
        delta = datetime.timedelta(seconds=expires_in)
        self.token_expiry = (client._UTCNOW() + delta)
    else:
        self.token_expiry = None
