Returns 'app_label.<perm>_<usermodulename>'. If standard ``auth.User`` is
    used, for 'change' perm this would return ``auth.change_user`` and if
    ``myapp.CustomUser`` is used it would return ``myapp.change_customuser``.

def get_user_permission_full_codename(perm):
    """
    Returns 'app_label.<perm>_<usermodulename>'. If standard ``auth.User`` is
    used, for 'change' perm this would return ``auth.change_user`` and if
    ``myapp.CustomUser`` is used it would return ``myapp.change_customuser``.
    """
    User = get_user_model()
    return '%s.%s_%s' % (User._meta.app_label, perm, User._meta.module_name)