Saml2AuthenticationRequestContext creation logic is not extensible at
the moment as it is provided inside of Saml2WebSsoAuthenticationRequestFilter.
This change enables to custom logic to be used when creating Saml2AuthenticationRequestContext by
taking the logic from the aforementioned filter to a seperate extensible
API by the name Saml2AuthenticationRequestContextResolver.
This provides following API contract and implementation:
- Saml2AuthenticationRequestContextResolver
- DefaultSaml2AuthenticationRequestContextResolver
Fixes gh-8360
8c0bdd50e2