Implements minimal SAML 2.0 login/authentication functionality with the
following feature set:
- Supports IDP initiated login at the default url of /login/saml2/sso/{registrationId}
- Supports SP initiated login at the default url of /saml2/authenticate/{registrationId}
- Supports basic java-configuration via DSL
- Provides an integration sample using Spring Boot
Not implemented with this MVP
- Single Logout
- Dynamic Service Provider Metadata
Fixes gh-6019