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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def list_credentials(self, user=None):
 """ Returns a user's non-password credentials. If no user is specified, the credentials for the currently authenticated user are returned. You cannot retrieve passwords by this or any other means. """

        if not user:
            user = self.user
        user_id = utils.get_id(user)
        uri = "users/%s/OS-KSADM/credentials" % user_id
        resp, resp_body = self.method_get(uri)
        return resp_body.get("credentials")