Passing login credentials to WP site from 3rd party site?

I have a question about accessing the site from a 3rd party site:

I have a plugin (Custom Login Lite) I use for access control on my WP site. I need users to access my site from a third party website where they will login to a members only area. Thereby when they click to go to my site, I need to have the UN and Password passed from that site to my WP site - thereby requiring no login at my WP site.

Is it as easy as simply sending a string along with the URL? If so, might you know how should the string be written?

Or is it more complex and something I don’t (yet) understand?

Thanks for reading a for any help you can provide. :slight_smile: