Failed to process OIDC Back-Channel Logout and cannot customize OIDC Back Channel Logout related classes

[Fix3dll]

OidcBackChannelLogoutAuthenticationProvider and related classes are protected final and doesn't accept custom classes because of next phases instanceof control. The main issue is that I'm using Keycloak, and when a back channel logout request is sent, Spring Boot can't process it. The log will be more descriptive:

DEBUG --- [0.0-8081-exec-1] .c.a.w.c.o.c.OidcBackChannelLogoutFilter : Failed to process OIDC Back-Channel Logout
org.springframework.security.oauth2.core.OAuth2AuthenticationException: An error occurred while attempting to decode the Jwt: Signed JWT rejected: Another algorithm expected, or no matching key(s) found
	at org.springframework.security.config.annotation.web.configurers.oauth2.client.OidcBackChannelLogoutAuthenticationProvider.decode(OidcBackChannelLogoutAuthenticationProvider.java:126)
	at org.springframework.security.config.annotation.web.configurers.oauth2.client.OidcBackChannelLogoutAuthenticationProvider.authenticate(OidcBackChannelLogoutAuthenticationProvider.java:103)
	at org.springframework.security.authentication.ProviderManager.authenticate(ProviderManager.java:182)
	at org.springframework.security.config.annotation.web.configurers.oauth2.client.OidcBackChannelLogoutFilter.doFilterInternal(OidcBackChannelLogoutFilter.java:104)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.wrapFilter(ObservationFilterChainDecorator.java:241)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.doFilter(ObservationFilterChainDecorator.java:228)
	at org.springframework.security.web.ObservationFilterChainDecorator$VirtualFilterChain.doFilter(ObservationFilterChainDecorator.java:138)
	at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90)
	at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.wrapFilter(ObservationFilterChainDecorator.java:241)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.doFilter(ObservationFilterChainDecorator.java:228)
	at org.springframework.security.web.ObservationFilterChainDecorator$VirtualFilterChain.doFilter(ObservationFilterChainDecorator.java:138)
	at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:82)
	at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:69)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.wrapFilter(ObservationFilterChainDecorator.java:241)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.doFilter(ObservationFilterChainDecorator.java:228)
	at org.springframework.security.web.ObservationFilterChainDecorator$VirtualFilterChain.doFilter(ObservationFilterChainDecorator.java:138)
	at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:62)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.wrapFilter(ObservationFilterChainDecorator.java:241)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.doFilter(ObservationFilterChainDecorator.java:228)
	at org.springframework.security.web.ObservationFilterChainDecorator$VirtualFilterChain.doFilter(ObservationFilterChainDecorator.java:138)
	at org.springframework.security.web.session.DisableEncodeUrlFilter.doFilterInternal(DisableEncodeUrlFilter.java:42)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.wrapFilter(ObservationFilterChainDecorator.java:241)
	at org.springframework.security.web.ObservationFilterChainDecorator$AroundFilterObservation$SimpleAroundFilterObservation.lambda$wrap$0(ObservationFilterChainDecorator.java:334)
	at org.springframework.security.web.ObservationFilterChainDecorator$ObservationFilter.doFilter(ObservationFilterChainDecorator.java:225)
	at org.springframework.security.web.ObservationFilterChainDecorator$VirtualFilterChain.doFilter(ObservationFilterChainDecorator.java:138)
	at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:233)
	at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:191)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
	at org.springframework.web.filter.ServletRequestPathFilter.doFilter(ServletRequestPathFilter.java:52)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
	at org.springframework.web.filter.CompositeFilter.doFilter(CompositeFilter.java:74)
	at org.springframework.security.config.annotation.web.configuration.WebSecurityConfiguration$CompositeFilterChainProxy.doFilter(WebSecurityConfiguration.java:319)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
	at org.springframework.web.servlet.handler.HandlerMappingIntrospector.lambda$createCacheFilter$4(HandlerMappingIntrospector.java:267)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
	at org.springframework.web.filter.CompositeFilter.doFilter(CompositeFilter.java:74)
	at org.springframework.security.config.annotation.web.configuration.WebMvcSecurityConfiguration$CompositeFilterChainProxy.doFilter(WebMvcSecurityConfiguration.java:240)
	at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:362)
	at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:278)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:138)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:138)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:138)
	at org.springframework.web.filter.ServerHttpObservationFilter.doFilterInternal(ServerHttpObservationFilter.java:110)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:138)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:138)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:165)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:88)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:113)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:83)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:72)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1774)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:973)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:491)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: org.springframework.security.oauth2.jwt.BadJwtException: An error occurred while attempting to decode the Jwt: Signed JWT rejected: Another algorithm expected, or no matching key(s) found
	at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.createJwt(NimbusJwtDecoder.java:188)
	at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.decode(NimbusJwtDecoder.java:142)
	at org.springframework.security.config.annotation.web.configurers.oauth2.client.OidcBackChannelLogoutAuthenticationProvider.decode(OidcBackChannelLogoutAuthenticationProvider.java:121)
	... 77 common frames omitted
Caused by: com.nimbusds.jose.proc.BadJOSEException: Signed JWT rejected: Another algorithm expected, or no matching key(s) found
	at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:394)
	at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:340)
	at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.createJwt(NimbusJwtDecoder.java:162)
	... 79 common frames omitted

Related spring-projects/spring-boot#48485
Spring Boot 3.5.8 and Spring Security 6.5.7