What implementation of SSO does Yandex use?

Question

Yandex

Tell me, what implementation of SSO does Yandex use?
How do they achieve authentication without redirects on the second service provider (when already authenticated in the passport)?
I looked in the direction of SAML, but could not achieve implementation without a redirect on the second service provider.
Thank you!

Answer 1

In .htaccess (in the 2nd level domain and in each 3rd level subdomain) add:

php_value session.save_path "/var/www/domain.tld/sessions/"
php_value session.cookie_domain .domain.tld

After a user is authorized on any domain.tld / *.domain.tld domain/subdomain, he will be "transparently" authorized on all other subdomains (and the root domain).