Provide extension points for authentication-related web filters (#5386)

#### What type of PR is this?

/kind feature
/area core
/area plugin
/milestone 2.13.x

#### What this PR does / why we need it:

See #5379 for more.

This PR provides three extension points:

- FormLoginSecurityWebFilter
- AuthenticationSecurityWebFilter
- AnonymousAuthenticationSecurityWebFilter

which could be extended by plugins easily.

#### Which issue(s) this PR fixes:

Fixes #5379

#### Special notes for your reviewer:

TBD.

#### Does this PR introduce a user-facing change?

```release-note
None
```

api/src/main/java/run/halo/app/security/AnonymousAuthenticationSecurityWebFilter.java

@@ -0,0 +1,13 @@
+package run.halo.app.security;
+
+import org.pf4j.ExtensionPoint;
+import org.springframework.web.server.WebFilter;
+
+/**
+ * Security web filter for anonymous authentication.
+ *
+ * @author johnniang
+ */
+public interface AnonymousAuthenticationSecurityWebFilter extends WebFilter, ExtensionPoint {
+
+}

api/src/main/java/run/halo/app/security/AuthenticationSecurityWebFilter.java

@@ -0,0 +1,13 @@
+package run.halo.app.security;
+
+import org.pf4j.ExtensionPoint;
+import org.springframework.web.server.WebFilter;
+
+/**
+ * Security web filter for normal authentication.
+ *
+ * @author johnniang
+ */
+public interface AuthenticationSecurityWebFilter extends WebFilter, ExtensionPoint {
+
+}

api/src/main/java/run/halo/app/security/FormLoginSecurityWebFilter.java

@@ -0,0 +1,13 @@
+package run.halo.app.security;
+
+import org.pf4j.ExtensionPoint;
+import org.springframework.web.server.WebFilter;
+
+/**
+ * Security web filter for form login.
+ *
+ * @author johnniang
+ */
+public interface FormLoginSecurityWebFilter extends WebFilter, ExtensionPoint {
+
+}

application/src/main/java/run/halo/app/plugin/ExtensionComponentsFinder.java

@@ -14,6 +14,7 @@
  * @since 2.0.0
  */
 @Component
+@Deprecated(forRemoval = true)
 public class ExtensionComponentsFinder {
     public static final String SYSTEM_PLUGIN_ID = "system";
     private final PluginManager pluginManager;

application/src/main/java/run/halo/app/plugin/extensionpoint/DefaultExtensionGetter.java

@@ -1,5 +1,6 @@
 package run.halo.app.plugin.extensionpoint;
 
+import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
 import java.util.Set;
@@ -86,6 +87,15 @@ public <T extends ExtensionPoint> Flux<T> getEnabledExtensionByDefinition(
             });
     }
 
+    @Override
+    public <T extends ExtensionPoint> Flux<T> getExtensions(Class<T> extensionPointClass) {
+        var extensions = new ArrayList<>(pluginManager.getExtensions(extensionPointClass));
+        applicationContext.getBeanProvider(extensionPointClass)
+            .orderedStream()
+            .forEach(extensions::add);
+        return Flux.fromIterable(extensions);
+    }
+
     @NonNull
     <T extends ExtensionPoint> List<T> getAllExtensions(Class<T> extensionPoint) {
         Stream<T> pluginExtsStream = pluginManager.getExtensions(extensionPoint)

application/src/main/java/run/halo/app/plugin/extensionpoint/ExtensionGetter.java

@@ -34,4 +34,13 @@ public interface ExtensionGetter {
      *                                  the {@link ExtensionPointDefinition}.
      */
     <T extends ExtensionPoint> Flux<T> getEnabledExtensionByDefinition(Class<T> extensionPoint);
+
+    /**
+     * Get all extensions according to extension point class.
+     *
+     * @param extensionPointClass extension point class
+     * @param <T> type of extension point
+     * @return a bunch of extension points.
+     */
+    <T extends ExtensionPoint> Flux<T> getExtensions(Class<T> extensionPointClass);
 }

application/src/main/java/run/halo/app/security/SecurityWebFiltersConfigurer.java

@@ -0,0 +1,68 @@
+package run.halo.app.security;
+
+import static org.springframework.security.config.web.server.SecurityWebFiltersOrder.ANONYMOUS_AUTHENTICATION;
+import static org.springframework.security.config.web.server.SecurityWebFiltersOrder.AUTHENTICATION;
+import static org.springframework.security.config.web.server.SecurityWebFiltersOrder.FORM_LOGIN;
+
+import lombok.Setter;
+import org.pf4j.ExtensionPoint;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+import org.springframework.security.config.web.server.ServerHttpSecurity;
+import org.springframework.security.web.server.WebFilterChainProxy;
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+import reactor.core.publisher.Mono;
+import run.halo.app.plugin.extensionpoint.ExtensionGetter;
+import run.halo.app.security.authentication.SecurityConfigurer;
+
+@Component
+public class SecurityWebFiltersConfigurer implements SecurityConfigurer {
+
+    private final ExtensionGetter extensionGetter;
+
+    public SecurityWebFiltersConfigurer(ExtensionGetter extensionGetter) {
+        this.extensionGetter = extensionGetter;
+    }
+
+    @Override
+    public void configure(ServerHttpSecurity http) {
+        http
+            .addFilterAt(
+                new SecurityWebFilterChainProxy(FormLoginSecurityWebFilter.class), FORM_LOGIN
+            )
+            .addFilterAt(
+                new SecurityWebFilterChainProxy(AuthenticationSecurityWebFilter.class),
+                AUTHENTICATION
+            )
+            .addFilterAt(
+                new SecurityWebFilterChainProxy(AnonymousAuthenticationSecurityWebFilter.class),
+                ANONYMOUS_AUTHENTICATION
+            );
+    }
+
+    public class SecurityWebFilterChainProxy implements WebFilter {
+
+        @Setter
+        private WebFilterChainProxy.WebFilterChainDecorator filterChainDecorator;
+
+        private final Class<? extends ExtensionPoint> extensionPointClass;
+
+        public SecurityWebFilterChainProxy(Class<? extends ExtensionPoint> extensionPointClass) {
+            this.extensionPointClass = extensionPointClass;
+            this.filterChainDecorator = new WebFilterChainProxy.DefaultWebFilterChainDecorator();
+        }
+
+        @Override
+        public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+            return extensionGetter.getExtensions(this.extensionPointClass)
+                .sort(AnnotationAwareOrderComparator.INSTANCE)
+                .cast(WebFilter.class)
+                .collectList()
+                .map(filters -> filterChainDecorator.decorate(chain, filters))
+                .flatMap(decoratedChain -> decoratedChain.filter(exchange));
+        }
+    }
+
+}

docs/extension-points/authentication.md

@@ -0,0 +1,77 @@
+# Halo 认证扩展点
+
+此前，Halo 提供了 AdditionalWebFilter 作为扩展点供插件扩展认证相关的功能。但是近期我们明确了 AdditionalWebFilter
+的使用用途，故不再作为认证的扩展点。
+
+目前，Halo 提供了三种认证扩展点：表单登录认证、普通认证和匿名认证。
+
+## 表单登录（FormLogin）
+
+示例如下：
+
+```java
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilterChain;
+import reactor.core.publisher.Mono;
+import run.halo.app.security.FormLoginSecurityWebFilter;
+
+@Component
+public class MyFormLoginSecurityWebFilter implements FormLoginSecurityWebFilter {
+
+  @Override
+  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+    // Do your logic here
+    return chain.filter(exchange);
+  }
+}
+
+```
+## 普通认证（Authentication）
+
+示例如下：
+
+```java
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilterChain;
+import reactor.core.publisher.Mono;
+import run.halo.app.security.AuthenticationSecurityWebFilter;
+
+@Component
+public class MyAuthenticationSecurityWebFilter implements AuthenticationSecurityWebFilter {
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+        // Do your logic here
+        return chain.filter(exchange);
+    }
+}
+```
+
+## 匿名认证（Anonymous Authentication
+
+示例如下：
+
+```java
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilterChain;
+import reactor.core.publisher.Mono;
+import run.halo.app.security.AnonymousAuthenticationSecurityWebFilter;
+
+@Component
+public class MyAnonymousAuthenticationSecurityWebFilter
+    implements AnonymousAuthenticationSecurityWebFilter {
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+        // Do your logic here
+        return chain.filter(exchange);
+    }
+}
+```
+
+我们在实现扩展点的时候需要注意：如果当前请求不满足认证条件，请一定要调用 `chain.filter(exchange)`，给其他 filter 留下机会。
+
+后续会根据需求实现其他认证相关的扩展点。