How to connect a site on Bitrkis and an application?

Question

Android

Greetings!
We are planning to develop a mobile application.
The application must be closely connected with the existing site - all content, and most importantly, authorization-registration only through the existing site database. Site on Bitrix.
With the usual content, everything is clear - we form JSON, transfer it to the application and output it.
But with authorization / registration is not very clear.
Tell me what to read for a general understanding of the process? For further communication with the developers. Google didn't help much.
Even just a set of abstruse words will do, then we’ll google everything ourselves :)

Answer 1

I think that the most important thing is the rest api, so that there are not just god knows what requests and json responses

Answer 2

The simplest - you can see here
https://dev.1c-bitrix.ru/api_help/main/reference/cuser
or its analogue in D7
Bitrix\Main\UserTable
+
https://gist.github.com/zmts/802dc9c3510d79fd40f9d ...