SAML Assertion from URI

Hi,

Do you know how can pick-up the SAML Response (SAML Assertion) by an URI.

Exemple :

Portail access : https://example.com

f5 APM as IdP for a "service-a"

User enter URL https://example.com/service-a/

User is connecting to portal on logon page

Then he receive the SAML RESPONSE

Regards,