There are 2 ways to specify endpoint acting as the Assertion Consumer Service in the Query Parameters for the AuthnRequest Server at the SP side.
You can use an index, or specify it explicitly. To illustrate :
In our setting, we've set the second, AssertionConsumerServiceURL.
We have our SP sending AuthnRequest with AssertionConsumerServiceURL: http://spid-test.com/path1/example.sso/SAML2/POST
However, we observe the IDP defaulting to different url: http://spid-test.com/path0/example.sso/SAML2/POST. How can we force
the explicitly use of the value from AssertionConsumerServiceURL ?