WIP: changes to support OpenID Connect RP-Initiated Logout 1.0 + Keycloak 17/18+

[wetted]

see: https://openid.net/specs/openid-connect-rpinitiated-1_0.html

closes Issue #1045

This is a work in progress and not necessarily a correct solution.

[wetted]

I just started getting a build error locally. I'm not sure yet what's going on. I am on vacation until 5 July, so I won't look at it before then.

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':security-oauth2:japiCmp'.
> A failure occurred while executing me.champeau.gradle.japicmp.JApiCmpWorkAction
   > Detected binary changes.
         - current: security-oauth2-3.6.2-SNAPSHOT.jar
         - baseline: micronaut-security-oauth2-3.6.1.jar.

[wetted]

I've made some progress. I'm down to three test failures, but the Keycloak 18 support still needs work.

Note that testcontainers-keycloak requires Java 11+ so the tests that use the Keycloak.groovy test util class are disabled for Java 8.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

83.9% Coverage
0.0% Duplication

[timyates]

Did some things on the Keycloak 18 side over here #1053