WordPress Login need to send api request to another webiste login

I have a WordPress website login pop-up:https://WordPress-537199-3013479.cloudwaysapps.com/stock-teaching/

and here is the website ( is called TT2) I want to send request: https://tt9898.net/
(Not built on WordPress and I don’t have access to the backend)

Here is our requirement: When people click the WordPress website button(image q1) , then it will appear a login pop up, after people type their login infomation. It will send the request to the TT2 website. So people can login TT2 website via WordPress

Attach file also have the api speci file, thank you!

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