How to close site display and open its display only in iframe?

Question

Frameworks

Tell me which way to look, you need a very simple ready-made solution.
Task:

There is a site site.ru
There is another site site2.ru

It is necessary to display the index.php page from the site2.ru site in the frame site.ru
while a direct request to site2.ru through the browser must be closed.

through htasse did not work, open for site.ru access permission and close for everyone. The user through the iframe is identified independently, with his own ip