keystone/api-ref/source/v3/samples/admin/application-credential-create-request.json

{
    "application_credential": {
        "name": "monitoring",
        "secret": "rEaqvJka48mpv",
        "description": "Application credential for monitoring.",
        "expires_at": "2018-02-27T18:30:59Z",
        "roles": [
            {"name": "Reader"}
        ],
        "unrestricted": false
    }
}