AssertionConsumerServiceIndex vs. AssertionConsumerURL

I am puzzled by the occurrence of these
two fields in an AuthNRequest. At the minimum there appears to be some
redundancy here: Why isn’t it always enough to set

AssertionConsumerURL to the right value?

Turning to the description of
AssertionConsumerServiceIndex in core, the sentence “It applies only to
profiles in which the request issuer is different from the presenter”
confuses me even further. Does this mean that the Web SSO profile does not use
this attribute? At the same time there is a reference to AssertionConsumerServiceIndex
within the SSO profile (lines 490). Perhaps the above sentence should  be deleted? Obviously, profiles that
mandate use of this index will do so explicitly and there is no need to discuss
it preemptively in core.

 

- prateek