Priority of AssertionConsumerServiceURL vs AssertionConsumerServiceIndex

Hi,

I have confusion regarding priority of AssertionConsumerServiceURL and AssertionConsumerServiceIndex.

AssertionConsumerServiceURL = ACS URL

AssertionConsumerServiceIndex = ACS Index

Consider the following scenario :

=> ACS URL in SAML Request : set

=> ACS Index in SAML Request: set

=> ACS URL is associated with SP configuration on IDP side but has different Index as compared to ACS Index in SAML Request.

=> The URL corresponding to ACS Index in SP configuration on IDP side is different w.r.t ACS URL in SAML Request.

Where will IDP send the SAML Response in this case ?

Also, is it required for IDP to set at least 1 ACS URL as default in SP configuration having multiple associated URLs ? Can IDP choose to have no ACS URL as default ?

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Regards,
Vipul