How to organize authorization in Telegram Bot in groups (PHP)?

Question

PHP

Good evening everyone!
The task was to develop a Telegram bot for site users, through which new articles from our site will be sent.
The user should receive mailings on articles of those categories that he has chosen in his personal account on the site.

In order to receive the newsletter, the user must log in to the telegram bot using the login and password from the site.
We want to add a button - log in, after clicking on which you will need to enter your login first, and then the password.

There are some questions that arise due to the inexperience of developing a tg bot.

How after clicking "Login" should my backend understand that the next request will be a login request? Does the telegram server store any statement for such a case? Then how do you initiate it? Or will you have to store statement in your database / cache, etc.? Or will I need to recheck the user's previous post each time? How is this case usually handled? Please share experience.

Thank you!