def login(self, user, password):
        """Authenticate a user in the server.

        :param user: Bugzilla user
        :param password: user password
        """
        params = {
            self.PBUGZILLA_LOGIN: user,
            self.PBUGZILLA_PASSWORD: password
        }

        try:
            r = self.call(self.RLOGIN, params)
        except requests.exceptions.HTTPError as e:
            cause = ("Bugzilla REST client could not authenticate user %s. "
                     "See exception: %s") % (user, str(e))
            raise BackendError(cause=cause)

        data = json.loads(r)
        self.api_token = data['token']
Authenticate a user in the server.

        :param user: Bugzilla user
        :param password: user password