Before you start the upgrade ... accordingly when upgrading to Spring Boot 3.0. Support for properties under spring.security.saml2.relyingparty.registration.{id}.identity-provider have been removed.
Spring is effectively less lenient in accepting fallback matches now, insisting on the resolvable part of the type signature to match even if the remaining part is leniently accepted with unresolvable ...
Some of that could be a few years out to be fair but they are interested in that and obviously, when we are here we can pull them in ... to be on staff by the Spring when they open the ...