d9d77bed82
The OIDC back-channel spec recommends using a logout token typ `logout+jwt` (see [here](https://openid.net/specs/openid-connect-backchannel-1_0-final.html#LogoutToken). Support of this type was recently added [on the servlet side]([on the Servlet side](https://github.com/spring-projects/spring-security/commit/9101bf1f7d5ad5d57ebfa2df78135704cdc19b23)), so back porting the same on the reactive side to close the gap. Closes gh-15702