How to subscribe to a label using a custom link, expecially in a Forum?

MattV and or Tarun I'm completely at a loss here. Can you show me specifically what to do? 

I'm happy to either do this in an endpoint or with JQuery, but I'm just not sure how to get the subscription part to work with an API call. 

I can get the basic call to work in JQuery using Tarun's script but beyond that I'm unable to understand what's required beyond this: 

    <@liaAddScript>
    ;(function ($) {
        $.ajax({
            type: "Get",
            url: "/api/2.0/search?q=SELECT * FROM users WHERE id='${user.id}'",

            success: function (data) {

                console.log('SubscribetoLabel', data)

            },
        });
    })(LITHIUM.jQuery);
    </@liaAddScript>

I don't understand how to include the rest that Tarun included.