def METHOD_NAME():
    """OIDC user by username query."""
    endpoint = OIDC_API['GROUP']
    query = request.args.get('query', None)
    if not query:
        return jsonify([])
    resp, status = _oidc(endpoint, query)
    group_mails = [f'{item["groupIdentifier"]}@cern.ch' for item in resp]
    return jsonify(group_mails)