How to receive post data from external redirects while maintaining login state in a mobile app(ionic)

This is an ionic mobile app.

I got confusion regarding integration with third party applications.

One such third party service works like this:

Our site redirects(using post request) to third party and people enter things like credit card in that site and it will redirect to our site with post request/data.

I tried using in app browser in ionic which successfully sent post request to third party site. But when it redirected back, if it redirects with get parameters, I would have captured them. But it is redirecting with post data and seems like ionic cannot capture post data.

So, thinking of capturing using server urls. But when I do with server urls, how do I maintain login state? Because people will be logged into the app, not server. So, this way, people might be asked to login to the server again?

So, what is the correct way to go here? Also, should I use token authentication or session authentication to make this work?

I am using Django backend for api by the way.