https://docs.spring.io/spring-authorization-server/docs/current/reference/html/index.html
https://docs.spring.io/spring-authorization-server/docs/current/reference/html/getting-started.html

https://github.com/Baeldung/spring-security-oauth/tree/master/oauth-resource-server

2023

2021
https://www.baeldung.com/spring-security-oauth-resource-server
2018
http://www.zakariaamine.com/2018-03-01/using-oauth2-in-spring-scopes
http://www.zakariaamine.com/2018-01-27/using-oauth2-in-spring
    https://github.com/zak905/oauth2-example


https://github.com/spring-projects/spring-security/blob/master/docs/manual/src/docs/asciidoc/_includes/servlet/oauth2/oauth2-resourceserver.adoc
https://github.com/spring-projects/spring-security/tree/master/samples/boot/oauth2resourceserver-opaque

https://github.com/spring-projects/spring-security/blob/master/samples/boot/oauth2resourceserver-opaque/src/main/java/sample/OAuth2ResourceServerSecurityConfiguration.java
https://github.com/spring-projects/spring-security/blob/master/samples/boot/oauth2resourceserver-opaque/src/main/resources/application.yml

OpaqueTokenIntrospector
https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/oauth2/server/resource/introspection/OpaqueTokenIntrospector.html
https://github.com/spring-projects/spring-security/blob/master/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/introspection/OpaqueTokenIntrospector.java

    https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/oauth2/core/OAuth2AuthenticatedPrincipal.html
    https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/core/GrantedAuthority.html


org.springframework.security.web.DefaultSecurityFilterChain : Creating filter chain: any request, [
    ...
    org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter@d1f74b8,
    ...

BearerTokenAuthenticationFilter
https://github.com/spring-projects/spring-security/blob/master/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/web/BearerTokenAuthenticationFilter.java

    @Configuration
    @EnableWebSecurity
    public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
        static class MyOpaqueTokenIntrospector implements OpaqueTokenIntrospector {
            public OAuth2AuthenticatedPrincipal introspect(String token) {
                Collection<GrantedAuthority> grantedAuthorities = List.of("SCOPE_some.api[group='stuff']").stream().map(SimpleGrantedAuthority::new).collect(Collectors.toList());
                return new DefaultOAuth2AuthenticatedPrincipal(Map.of("active", true), grantedAuthorities);
            }
        }
        private MyOpaqueTokenIntrospector mybIntrospector() {
            return new MyOpaqueTokenIntrospector();
        }
        @Override
        protected void configure(HttpSecurity http) throws Exception {
            //@formatter:off
            http
                    .cors().disable()
                    .csrf().disable()
                    .sessionManagement().disable()
                    .authorizeRequests(authorizeRequests ->
                        authorizeRequests
                            // TODO: fix group names
                            .antMatchers(HttpMethod.GET, "/v1/**").hasAuthority("SCOPE_some.api[group=''stuff'']")
                            .antMatchers(HttpMethod.POST, "/v1/**").hasAuthority("SCOPE_some.api[group=''stuff'']")
                            .anyRequest().permitAll()
                    )
                    .oauth2ResourceServer(oauth2ResourceServer ->
                        oauth2ResourceServer
                            .opaqueToken(opaqueToken -> opaqueToken
                                .introspector(myIntrospector())
                            )
                    );
            //@formatter:on
        }
    }

to-find-replacement-for:
https://github.com/spring-projects/spring-security-oauth/blob/master/spring-security-oauth2/src/main/java/org/springframework/security/oauth2/provider/token/RemoteTokenServices.java
https://github.com/spring-projects/spring-security-oauth/blob/master/spring-security-oauth2/src/main/java/org/springframework/security/oauth2/provider/token/DefaultAccessTokenConverter.java
    extractAuthentication