Add before and after security web filters (#6297)

#### What type of PR is this?

/kind feature
/kind api-change
/area core
/area plugin

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

This PR adds `BeforeSecurityWebFilter` and `AfterSecurityWebFilter` extension points. See halo-sigs/plugin-page-cache#4 (comment) for more.

Now, we can do something before and after authenticating.

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

```release-note
添加认证授权的前置和后置处理器扩展点
```

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

@@ -0,0 +1,14 @@
+package run.halo.app.security;
+
+import org.pf4j.ExtensionPoint;
+import org.springframework.web.server.WebFilter;
+
+/**
+ * Security web filter for after security.
+ *
+ * @author johnniang
+ * @since 2.18
+ */
+public interface AfterSecurityWebFilter extends WebFilter, ExtensionPoint {
+
+}

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

@@ -0,0 +1,14 @@
+package run.halo.app.security;
+
+import org.pf4j.ExtensionPoint;
+import org.springframework.web.server.WebFilter;
+
+/**
+ * Security web filter for before security.
+ *
+ * @author johnniang
+ * @since 2.18
+ */
+public interface BeforeSecurityWebFilter extends WebFilter, ExtensionPoint {
+
+}

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

@@ -2,7 +2,9 @@
 
 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.FIRST;
 import static org.springframework.security.config.web.server.SecurityWebFiltersOrder.FORM_LOGIN;
+import static org.springframework.security.config.web.server.SecurityWebFiltersOrder.LAST;
 
 import lombok.Setter;
 import org.pf4j.ExtensionPoint;
@@ -30,7 +32,12 @@ public SecurityWebFiltersConfigurer(ExtensionGetter extensionGetter) {
     public void configure(ServerHttpSecurity http) {
         http
             .addFilterAt(
-                new SecurityWebFilterChainProxy(FormLoginSecurityWebFilter.class), FORM_LOGIN
+                new SecurityWebFilterChainProxy(BeforeSecurityWebFilter.class),
+                FIRST
+            )
+            .addFilterAt(
+                new SecurityWebFilterChainProxy(FormLoginSecurityWebFilter.class),
+                FORM_LOGIN
             )
             .addFilterAt(
                 new SecurityWebFilterChainProxy(AuthenticationSecurityWebFilter.class),
@@ -39,7 +46,12 @@ public void configure(ServerHttpSecurity http) {
             .addFilterAt(
                 new SecurityWebFilterChainProxy(AnonymousAuthenticationSecurityWebFilter.class),
                 ANONYMOUS_AUTHENTICATION
-            );
+            )
+            .addFilterAt(
+                new SecurityWebFilterChainProxy(AfterSecurityWebFilter.class),
+                LAST
+            )
+        ;
     }
 
     public class SecurityWebFilterChainProxy implements WebFilter {

docs/extension-points/authentication.md

@@ -27,6 +27,7 @@ public class MyFormLoginSecurityWebFilter implements FormLoginSecurityWebFilter
 }
 
 ```
+
 ## 普通认证（Authentication）
 
 示例如下：
@@ -41,11 +42,11 @@ 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);
-    }
+  @Override
+  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+    // Do your logic here
+    return chain.filter(exchange);
+  }
 }
 ```
 
@@ -62,16 +63,56 @@ import run.halo.app.security.AnonymousAuthenticationSecurityWebFilter;
 
 @Component
 public class MyAnonymousAuthenticationSecurityWebFilter
-    implements AnonymousAuthenticationSecurityWebFilter {
+        implements AnonymousAuthenticationSecurityWebFilter {
+
+  @Override
+  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+    // Do your logic here
+    return chain.filter(exchange);
+  }
+}
+```
+
+## 前置过滤器（BeforeSecurityWebFilter）
+
+主要用于在进行认证之前的一些处理。需要注意的是，当前过滤器中无法直接通过 ReactiveSecurityContextHolder 获取
+SecurityContext。示例如下：
+
+```java
+public class MyBeforeSecurityWebFilter implements BeforeSecurityWebFilter {
 
-    @Override
-    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
-        // Do your logic here
-        return chain.filter(exchange);
-    }
+  @Override
+  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+    // Do your logic here
+    return chain.filter(exchange);
+  }
 }
 ```
 
+## 后置过滤器（AfterSecurityWebFilter）
+
+主要用于进行认证之后的一些处理。在当前过滤器中，可以通过 ReactiveSecurityContextHolder 获取 SecurityContext。示例如下：
+
+```java
+public class MyAfterSecurityWebFilter implements AfterSecurityWebFilter {
+
+  @Override
+  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+    return ReactiveSecurityContextHolder.getContext()
+            .switchIfEmpty(Mono.defer(() -> {
+              // do something...
+              return chain.filter(exchange).then(Mono.empty());
+            }))
+            .flatMap(securityContext -> {
+              // do something...
+              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。