Understanding flow / federation

[Cantor, Scott]

Several of your questions keep mentioning trying to pass control from the
IdP to another IdP. Shibboleth does not support that out of the box, and
nothing in relying-party.xml has anything to do with that use case
whatsoever.

That's called IdP proxying. You can either construct such a gateway
yourself by writing custom extensions for various things and combining
other Shibboleth pieces together, or you would have to look at an
alternative implementation that is more targeted at that proxying use case.

I don't think you're equipped to write a lot of code based on your
questions, so you probably should consider alternatives if that's your use
case.

-- Scott