How to restrict the site to users, but leave it available for example for Samara?

Question

PHP

It is necessary to prohibit viewing the site to Internet users from different cities and regions, but leave it available for Samara.
An example on YouTube Red
when entering the site, we are told that the site is not yet available for our country, but it is available
for America.

Answer 1

Google "how to find out the city by IP".
However, whoever needs it will bypass it through vpn / tor.

Answer 2

GeoIP. But be prepared for the fact that not all providers may have the correct location. This used to be the case with mobile devices.

Answer 3

GeoIP (there are a lot of classes for PHP), well, or we once did a city test of 100 questions, 5 questions for registration, which only a local could answer, but our city was small - 200,000 people.