How to do a json post call to log in my users directly into the app with a link just like amazon or flipkart?

I want to log my users into the into my apk via Deeplink. I don’t want them to log into my app again.
Just like flipkart or Amazon , when you see a link on your browser and you click on it you are redirected to that page in the app where you are already logged in .

My deeplink functionality is working fine. I don’t know how to send a json post call which will have my token and operator ID ? Can somebody please tell me Where should i get started with this?