Nodejs, Express. Is there a way to store/get what POST params are required in an endpoint to show to the client?

I'm writing some test page to debug my API and expose it neatly.

Using Express app.routes I can get a neat list of all the endpoints my application implements, so I can show to the users the list of possible POST requests.

However, most of them require some POST parameters, which the server obtains from the requests in this way, for example (/api/ping requires a "ping" POST parameter):

app.post("/api/ping", function(req, res) //
{
    var ping = req.param('ping');

    if( ping ) {    
        res.out.message = "Pong";
    } else {
        res.out.message = "Ping missing";
    }

    return exports.respond(res);
});

I noticed that app.routes has a "keys" and a "params" keys in the endpoints list, but I think this seems to be used only for parameters that are in the path (for example "userid" as parameter when someone requests for the "/user/:userid" path). I believe express calls these stored parameters "pre-conditions".

Is there any way to add preconditions like these to express app for POST parameters so that they are also shown in the app.routes object and I can display neatly which parameters are required for which endpoint?