OAuth request token url returns “500 Internal Server Error”

According to https://github.com/openstreetmap/openstreetmap-website/issues/1049#issuecomment-136450085 the problem is not an unknown client but an invalid signature.

Hi, I am testing Openstreetmaps OAuth using an Android app. This is the related code:

    ...
    OkHttpClient client = new OkHttpClient();

    String url3 = "https://master.apis.dev.openstreetmap.org/oauth/request_token";

    RequestBody formBody = new FormBody.Builder()
            .add("consumer_key", client_id)
            .add("consumer_secret", client_secret)
            .add("callback", "https://spark71.com")
            .build(); 
    Request request = new Request.Builder()
            .url(url3)
            .post(formBody)
            .build();

    client.newCall(request)
            .enqueue(new Callback() {
                @Override
                public void onFailure(final Call call, IOException e) {

...

Thank you

Jesus Picornell