Add Single Logout to SAML 2.0 configuration properties

[marcusdacoregio]

SAML 2.0 Single Logout support was added in Spring Security 5.6.

In order to activate the feature, each configured RelyingPartyRegistration must set a singleLogoutServiceLocation. Currently, there is no way to provide the property using Spring Boot.

The configuration may look like this:

spring:
    security:
        saml2:
            relyingparty:
                one:
                    ...
                    slo:
                        location: /logout/saml2/slo
                        response-location: /logout/saml2/slo
                        binding: POST
                    identityprovider:
                        ...
                        singlelogout:
                            location: ...
                            response-location: ...
                            binding: POST

[wilkinsona]

Thanks, @marcusdacoregio. Could you please comment on #30128 with some guidance for the other properties that may be missing?