While configuring SSO with SAML 2.

Explanation (Adobe Docs Reference):

When configuring SAML SSO with AEM, the dispatcher must allow POST requests to the saml_login endpoint. If blocked, AEM redirects endlessly back to the IDP. This is done by allowing the POST request in filters.any.

Adobe Documentation:

“For SAML authentication to work with AEM behind a Dispatcher, you must configure the dispatcher filter to allow POST requests to /saml_login. Otherwise, authentication attempts will loop infinitely.”

— AEM Dispatcher and SAML Authentication Configuration