Saml2WebSsoAuthenticationFilter adds authentication details

[Kehrlann]

Closes gh-7722.

[Kehrlann]

Hi there!

We've been needing authentication details in our product, specifically WebAuthenticationDetails. I saw gh-7722 and decided to submit this.

Notes:

1. I added a test in Saml2WebSsoAuthenticationFilterTests + OpenSaml4AuthenticationProviderTests rather than more integration-style Saml2LoginConfigurerTests, but I am unsure whether it is the right place. Maybe they should be in both?
   1. This being the default setup, I feel it does not have a place in the Saml2LoginConfigurerTests , but on the other hand an integration tests would give greater confidence that it actually works.
2. In Saml2WebSsoAuthenticationFilter there is a cast to AbstractAuthenticationToken
   1. Technically the authentication converter returns a Saml2AuthenticationToken by default.
   2. However, that is not required.
   3. I can't really imagine a setup where a user provides both their own converter AND their own auth provider (they should probably provide their own filter if they do this), and do not even rely on AbstractAuthenticationToken...
   4. But I with a type check just in case and upcast to the simplest possible thing. Please let me know if that is too cautious.
3. I have not backported this change to OpenSamlAuthenticationProvider as it is deprecated, but I can trivially port it back if required.

[marcusdacoregio]

Hi @Kehrlann, thank you very much for the PR. I've left some feedback inline.

[marcusdacoregio]

Thank you @Kehrlann.

I've left a couple more suggestions in line. Once you fix them we can merge the PR!

[marcusdacoregio]

Thank you very much @Kehrlann. This is now merged into main.