Saml2 metadata includes SingleLogoutService even if saml2 logout is disabled / not configured

[dvanbler]

Describe the bug
When accessing a saml2 relying party's metadata via the Saml2MetadataFilter endpoint, the downloaded metadata.xml file includes a SingeLogoutService element even though I have disabled or not configured saml2 logout.

To Reproduce

• in a WebSecurityConfigurerAdapter, disable saml2 logout: http.saml2Logout().disable()
• configure a saml2 relying party - do not specify any logout configuration for either the relying party or the asserting party.
• configure the saml2 metadata filter
• visit the saml2 metadata url and inspect the downloaded metadata.xml
• notice that the metadata contains a SingleLogoutService element

Expected behavior
If saml2 logout is disabled, then relying party metadata should not advertise a single logout service.

[jzheaux]

If saml2 logout is disabled, then relying party metadata should not advertise a single logout service.

While I see your point, we can't do as you describe. The reason is that the DSL is setting up a filter chain while the relying party registration is potentially coming from an external repository. It would be too aggressive for the DSL to try and configure your repository.

That said, I believe there are two issues that can be addressed here in order to help:

First, this ticket alerted me to the issue that the filter chain does not support a null single logout service location, which is a bug. Since each registration can represent a single tenant, it's reasonable to have saml2Logout enabled in the filter chain, but have single logout un-configured for certain tenants. I've created #10674 to address this.

Second, it's odd that any application not wanting to use the SAML 2.0 Logout feature would need to remove the single logout service location from each registration. Since it's optional, it should instead be provided. Let's use this issue to address this.