API of a SIP web client to put in my website

I have a voip Asterisk server that use SIP protocol to connect with the clients, normally I use sofphones, IP telephones or some App to make calls with this server. Now I need of implement a new feature in my website that is to make calls on-line in a web application, could only add a box with the field to number dialed that will make the call. I need a developer that could reuse some API to connect in my voip server and make calls. I will provide one user and password to connect in the server, the solution should to be put in my Wordpress website.