How to log in to another site (PHP)?

Question

PHP

There is an authorization form on the "other" site, two fields - login, password. Data known to me.
I need to create a link/button on my site, by clicking on which I opened "another" site already authorized.
The problem is that the "other" site returns 403 if no referrer is passed from its authentication page.
How can I be logged in to the "other" site?
PS On the "other" site, I can't make any changes.

Answer 1

emulate this. php curl, save all response cookies, you can referrer and replace.