Did you mean https://auth0.com ?

If yes then Elgg integration isn't so easy and you may need to hire developers.

There is no turnkey solution for Elgg.

yes. https://auth0.com. And I was preparing myself for your answer. Seems like no easy integration so I'm working on the customizations myself.

Look at this plugin and this outdated plugin for your Elgg 1.8

Will Oembed also display images/gif along with Video on Output?

Noticed this in/mod/oembed/views/default/oembed/js elgg_after.php

<?php
if (0): ?><script><?php endif; ?>

<?php // inlining the script here so it will be cached with js/elgg
readfile(dirname(dirname(dirname(dirname(__DIR__)))) . '/lib/jquery.oembed.min.js'); ?>

$(function() {
    // don't display embeds in comments
    $("a[title^=oembed]:not(.elgg-comments a)").append(' (loading...)').oembed(null, {
        embedMethod:'fill',
        maxWidth: 500
    });
});

How would that be modified for showing Oembed output in comments?

Thanks fr pointing the direction... This is for 1.12 server... Oembed v1.8 will function.

Read this tutorial