How to use the federation.credentials.src.trust.hierarchy.AuthInfo function in federation

def get_auth_info(self, xrn):
        hrn, type = urn_to_hrn(xrn)
        if not self.auth_exists(hrn):
            raise MissingAuthority(hrn)

        (directory, gid_filename, privkey_filename, ) = \
            self.get_auth_filenames(hrn)

        auth_info = AuthInfo(hrn, gid_filename, privkey_filename)

        # check the GID and see if it needs to be refreshed
        gid = auth_info.get_gid_object()
        gid_refreshed = self.refresh_gid(gid)
        if gid != gid_refreshed:
            auth_info.update_gid_object(gid_refreshed)

        return auth_info