<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def current_user_id():
 """ This method returns the user id retrieved from jwt token data attached to the current flask app's context """

    jwt_data = get_jwt_data_from_app_context()
    user_id = jwt_data.get('id')
    PraetorianError.require_condition(
        user_id is not None,
        "Could not fetch an id for the current user",
    )
    return user_id