@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    http
        .oauth2Login(oauth2 -> oauth2
            .authorizationEndpoint(authorization -> authorization.authorizationRequestResolver()
                ...)
           .tokenEndpoint(token -> token.accessTokenResponseClient()
                ...)
           .userInfoEndpoint(userInfo -> userInfo.userService()
                ...)
        );
   return http.build();
    }

public final class DefaultOAuth2AuthorizationRequestResolver implements OAuth2AuthorizationRequestResolver {
    ...
    private Consumer<OAuth2AuthorizationRequest.Builder> authorizationRequestCustomizer = (customizer) -> {};
    ...         
    private OAuth2AuthorizationRequest resolve(HttpServletRequest request, String registrationId,
           String redirectUriAction) {
        if (registrationId == null) {
           return null;
        }
        ClientRegistration clientRegistration = this.clientRegistrationRepository.findByRegistrationId(registrationId);
        if (clientRegistration == null) {
           throw new InvalidClientRegistrationIdException("Invalid Client Registration with Id: " + registrationId);
        }
        OAuth2AuthorizationRequest.Builder builder = getBuilder(clientRegistration);
        ...
        this.authorizationRequestCustomizer.accept(builder); // 可在此注入定制逻辑
        return builder.build();
    }
    ...
}

public OAuth2AuthorizationRequest build() {
    ...
    authorizationRequest.authorizationRequestUri = StringUtils.hasText(this.authorizationRequestUri)
          ? this.authorizationRequestUri : this.buildAuthorizationRequestUri(); // 如果没有额外设置，最终构造URL的方法是buildAuthorizationRequestUri
    return authorizationRequest;
}
private String buildAuthorizationRequestUri() {
    Map<String, Object> parameters = getParameters(); 
    this.parametersConsumer.accept(parameters); // 扩展点
    MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<>();
    parameters.forEach((k, v) -> queryParams.set(encodeQueryParam(k), encodeQueryParam(String.valueOf(v)))); 
    UriBuilder uriBuilder = this.uriBuilderFactory.uriString(this.authorizationUri).queryParams(queryParams);
    return this.authorizationRequestUriFunction.apply(uriBuilder).toString(); // 扩展点
}

public final class DefaultAuthorizationCodeTokenResponseClient implements OAuth2AccessTokenResponseClient<OAuth2AuthorizationCodeGrantRequest> {
    ...
    private Converter<OAuth2AuthorizationCodeGrantRequest, RequestEntity<?>> requestEntityConverter = new ClientAuthenticationMethodValidatingRequestEntityConverter<>(
          new OAuth2AuthorizationCodeGrantRequestEntityConverter());
    private RestOperations restOperations;
   
    public DefaultAuthorizationCodeTokenResponseClient() {
        RestTemplate restTemplate = new RestTemplate(
              Arrays.asList(new FormHttpMessageConverter(), new OAuth2AccessTokenResponseHttpMessageConverter())); // 定制OAuth2AccessTokenResponseHttpMessageConverter
        restTemplate.setErrorHandler(new OAuth2ErrorResponseErrorHandler());
        this.restOperations = restTemplate;
    }
    @Override
    public OAuth2AccessTokenResponse getTokenResponse(OAuth2AuthorizationCodeGrantRequest authorizationCodeGrantRequest) {
       ...
       RequestEntity<?> request = this.requestEntityConverter.convert(authorizationCodeGrantRequest); //生成请求实体对象，利用这个converter注入定制逻辑
       ResponseEntity<OAuth2AccessTokenResponse> response = getResponse(request);
       OAuth2AccessTokenResponse tokenResponse = response.getBody();
       ...
       return tokenResponse;
    }
    private ResponseEntity<OAuth2AccessTokenResponse> getResponse(RequestEntity<?> request) {
       ...
          return this.restOperations.exchange(request, OAuth2AccessTokenResponse.class);
    }
    ...
}

public class DefaultOAuth2UserService implements OAuth2UserService<OAuth2UserRequest, OAuth2User> {
    ...
    private Converter<OAuth2UserRequest, RequestEntity<?>> requestEntityConverter = new OAuth2UserRequestEntityConverter();
    private RestOperations restOperations;
    public DefaultOAuth2UserService() {
       RestTemplate restTemplate = new RestTemplate();
       restTemplate.setErrorHandler(new OAuth2ErrorResponseErrorHandler());
       this.restOperations = restTemplate;
    }
   
    @Override
    public OAuth2User loadUser(OAuth2UserRequest userRequest) throws OAuth2AuthenticationException {
        Assert.notNull(userRequest, "userRequest cannot be null");
        String userNameAttributeName = getUserNameAttributeName(userRequest);
        RequestEntity<?> request = this.requestEntityConverter.convert(userRequest);
        ResponseEntity<Map<String, Object>> response = getResponse(userRequest, request);
        OAuth2AccessToken token = userRequest.getAccessToken();
        Map<String, Object> attributes = this.attributesConverter.convert(userRequest).convert(response.getBody());
        Collection<GrantedAuthority> authorities = getAuthorities(token, attributes);
        return new DefaultOAuth2User(authorities, attributes, userNameAttributeName);
    }
    ...
}

@Slf4j
@EnableWebSecurity
@Configuration
public class SpringSecurityConfiguration {
    @Resource
    private ClientRegistrationRepository clientRegistrationRepository;
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.oauth2Login(oauth2 -> oauth2
                .authorizationEndpoint(authorization -> authorization.authorizationRequestResolver(authorizationRequestResolver(clientRegistrationRepository)))
                .tokenEndpoint(token -> token.accessTokenResponseClient(accessTokenResponseClient()))
                .userInfoEndpoint(userInfo -> userInfo.userService(userService()))
        );
        DefaultSecurityFilterChain filterChain = http.build();
        filterChain.getFilters().stream().map(Object::toString).forEach(log::info);
        return filterChain;
    }
    private OAuth2AuthorizationRequestResolver authorizationRequestResolver(ClientRegistrationRepository clientRegistrationRepository) {
        String authorizationRequestBaseUri = OAuth2AuthorizationRequestRedirectFilter.DEFAULT_AUTHORIZATION_REQUEST_BASE_URI;
        // 参考框架内默认的实例构造方法
        DefaultOAuth2AuthorizationRequestResolver resolver = new DefaultOAuth2AuthorizationRequestResolver(clientRegistrationRepository, authorizationRequestBaseUri);
        // 设置OAuth2AuthorizationRequest.builder的定制逻辑
        resolver.setAuthorizationRequestCustomizer(builder -> builder.parameters(this::parametersConsumer).authorizationRequestUri(this::authorizationRequestUriFunction));
        return resolver;
    }
    private void parametersConsumer(Map<String, Object> parameters) {
        Object clientId = parameters.get(OAuth2ParameterNames.CLIENT_ID);
        Object redirectUri = parameters.get(OAuth2ParameterNames.REDIRECT_URI);
        Object responseType = parameters.get(OAuth2ParameterNames.RESPONSE_TYPE);
        Object scope = parameters.get(OAuth2ParameterNames.SCOPE);
        Object state = parameters.get(OAuth2ParameterNames.STATE);
        // 清除掉原来所有的参数
        parameters.clear();
        // 重新调整顺序
        parameters.put("appid", clientId);// 修改clientId参数名称为appid
        parameters.put(OAuth2ParameterNames.REDIRECT_URI, redirectUri);
        parameters.put(OAuth2ParameterNames.RESPONSE_TYPE, responseType);
        parameters.put(OAuth2ParameterNames.SCOPE, scope);
        parameters.put(OAuth2ParameterNames.STATE, state);
    }
    private URI authorizationRequestUriFunction(UriBuilder builder) {
        builder.fragment("wechat_redirect");// 添加#wechat_redirect
        return builder.build();
    }
   
    private OAuth2AccessTokenResponseClient<OAuth2AuthorizationCodeGrantRequest> accessTokenResponseClient() {
        DefaultAuthorizationCodeTokenResponseClient client = new DefaultAuthorizationCodeTokenResponseClient();
        // 注入自定义WechatOAuth2AuthorizationCodeGrantRequestEntityConverter
        client.setRequestEntityConverter(new WechatOAuth2AuthorizationCodeGrantRequestEntityConverter()); 
        // 创建一个OAuth2AccessTokenResponseHttpMessageConverter对象，设置支持的MediaType为text/plain
        OAuth2AccessTokenResponseHttpMessageConverter messageConverter = new OAuth2AccessTokenResponseHttpMessageConverter();
        messageConverter.setSupportedMediaTypes(List.of(MediaType.TEXT_PLAIN)); 
        messageConverter.setAccessTokenResponseConverter(new WechatOAuth2AccessTokenResponseConverter());
        // 其他配置照搬源码
        RestTemplate restTemplate = new RestTemplate(Arrays.asList(new FormHttpMessageConverter(), messageConverter));
        restTemplate.setErrorHandler(new OAuth2ErrorResponseErrorHandler());
        client.setRestOperations(restTemplate);
        return client;
    }
    private static class WechatOAuth2AccessTokenResponseConverter implements Converter<Map<String, Object>, OAuth2AccessTokenResponse> {
        private static final DefaultMapOAuth2AccessTokenResponseConverter delegate = new DefaultMapOAuth2AccessTokenResponseConverter();
        //响应中缺少token_type字段，为避免报错默认填充，剩余部分依然委托给默认的DefaultMapOAuth2AccessTokenResponseConverter处理
        @Override
        public OAuth2AccessTokenResponse convert(Map<String, Object> source) {
            source.put(OAuth2ParameterNames.TOKEN_TYPE, OAuth2AccessToken.TokenType.BEARER.getValue()); 
            return delegate.convert(source);
        }
    }
    // 无法直接实现接口，不过可以继承OAuth2AuthorizationCodeGrantRequestEntityConverter
    private static class WechatOAuth2AuthorizationCodeGrantRequestEntityConverter extends OAuth2AuthorizationCodeGrantRequestEntityConverter {
        //参考父类的源码，依葫芦画瓢重写createParameters方法，根据微信的文档，依次添加appid，secret，grant_type，code这四个参数
        @Override
        protected MultiValueMap<String, String> createParameters(OAuth2AuthorizationCodeGrantRequest authorizationCodeGrantRequest) {
            ClientRegistration clientRegistration = authorizationCodeGrantRequest.getClientRegistration();
            OAuth2AuthorizationExchange authorizationExchange = authorizationCodeGrantRequest.getAuthorizationExchange();
            MultiValueMap<String, String> parameters = new LinkedMultiValueMap<>();
            parameters.add("appid", clientRegistration.getClientId());
            parameters.add("secret", clientRegistration.getClientSecret());
            parameters.add(OAuth2ParameterNames.GRANT_TYPE, authorizationCodeGrantRequest.getGrantType().getValue());
            parameters.add(OAuth2ParameterNames.CODE, authorizationExchange.getAuthorizationResponse().getCode());
            return parameters;
        }
    }
    private OAuth2UserService<OAuth2UserRequest, OAuth2User> userService() {
        DefaultOAuth2UserService userService = new DefaultOAuth2UserService();
        // 注入自定义的requestEntityConverter
        userService.setRequestEntityConverter(new WechatOAuth2UserRequestEntityConverter());
        // 创建一个MappingJackson2HttpMessageConverter对象，同样设置支持的MediaType为text/plain
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
        messageConverter.setSupportedMediaTypes(List.of(MediaType.TEXT_PLAIN));
        RestTemplate restTemplate = new RestTemplate(List.of(messageConverter));
        restTemplate.setErrorHandler(new OAuth2ErrorResponseErrorHandler());
        userService.setRestOperations(restTemplate);
        return userService;
    }
    private static class WechatOAuth2UserRequestEntityConverter implements Converter<OAuth2UserRequest, RequestEntity<?>> {
        // 根据微信文档，在请求地址中拼接上access_token和openid两个参数
        @Override
        public RequestEntity<?> convert(OAuth2UserRequest userRequest) {
            ClientRegistration clientRegistration = userRequest.getClientRegistration();
            URI uri = UriComponentsBuilder.fromUriString(clientRegistration.getProviderDetails().getUserInfoEndpoint().getUri())
                    .queryParam(OAuth2ParameterNames.ACCESS_TOKEN, userRequest.getAccessToken().getTokenValue())
                    .queryParam("openid", userRequest.getAdditionalParameters().get("openid"))
                    .build()
                    .toUri();
            return new RequestEntity<>(HttpMethod.GET, uri);
        }
    }
}

@RestController
public class UserController {
    @GetMapping("/user")
    public String user() {
        String username = SecurityContextHolder.getContext().getAuthentication().getName();
        return "Hello " + username;
    }
   
}