Add support for getting end_session_endpoint from OIDC Configuration

[mraible]

Summary

Okta has an end_session_endpoint property that can be used to construct a global logout that happens on the client. Example code here.

It would be nice if Spring Security's OIDC support provided a way to access this end_session_endpoint. This property is present in ./well-known/openid-configuration.

Version

5.1.0.BUILD-SNAPSHOT

Sample

https://github.com/oktadeveloper/okta-spring-boot-react-crud-example/compare/spring-security-5.1

[jgrandja]

Related #5350

[jgrandja]

@mraible Thanks for the report!

There currently is OpenID Connect Discovery code in OidcConfigurationProvider. One of our tasks is to extract that bit of code so it can be re-used in other places within Spring Security.

We'll get this in for 5.1