From 254062c161354143525318e3ff36c79722e34af3 Mon Sep 17 00:00:00 2001
From: asahi <mikiyashiki@outlook.com>
Date: Tue, 12 Mar 2024 00:41:28 +0800
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+# Spring Security
+Spring Security提供了authentication（认证）、authorization（授权）、protection against common attacks（防御常见攻击）的功能。
+
+Spring Security提供了针对如下常见攻击的防御：
+- CSRF
+- Http Headers
+- Http Requests
+
+## 默认自动装配
+当web项目引入Spring Security依赖后，如果不做任何特殊处理，Spring Security会默认为项目配置一个登录校验。当用户没有进行登录而访问页面时，会拦截用户请求返回一个登录页，在用户登录成功之后，再会将url重定向到用户先前请求的页面。
+
+### Spring Security默认为项目做的操作
+1. 保护web项目的url，Spring Security要求与http接口进行的任何交互都需要进行身份认证
+2. Spring Security会在web项目启动时生成一个默认的用户，用户名为user，用户密码会通过日志打出
+3. Spring Security会为项目生成默认的登录和注销页面，并提供了基本登录流程和注销流程
+4. 对于http请求，如果在没有进行身份认证的情况下，会重定向到登录页面
+
+## Spring Security底层结构
+Spring Security底层通过Filter链来实现。
+
+### DelegatingFilterProxy
+spring boot提供了Filter的实现类DelegatingFilterProxy，该类将实际的过滤逻辑委托给另一个filter bean对象。
+
+通过DelegatingFilterProxy，可以将servlet container和spring容器结合起来，将DelegatingFilterProxy对象作为filter注册到servlet container中，然后DelegatingFilterProxy把实际过滤逻辑委托给spring context中的bean对象，如此可以通过向spring容器中注册bean对象来自定义filter chain逻辑。
+
+### SecurityFilterChain
+DelegationFilterProxy将filter逻辑委托给了FilterChainProxy。
+
+而FilterProxyChain则是包含了SecurityFilterChain（并且可以包含多个SecurityFilterChain）。SecurityFilterChain中包含的才是多个filter bean对象。
+
+如果FilterChainProxy中注册了多个SecurityFilterChain，那么将由FilterChainProxy来决定实际调用哪个SecurityFilterChain。只有匹配的第一个SecurityFilterChain会被实际调用。
+
+> 如果当spring容器中存在多个SecurityFilterChian bean对象，那么可以通过@Order注解来指定SecurityFilterChain bean对象的顺序，从而调整不同SecurityFilterChain的优先级
+
+示例如下：
+```java
+@Configuration
+@EnableWebSecurity
+public class SecurityConfig {
+
+    @Bean
+    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
+        http
+            .csrf(Customizer.withDefaults())
+            .authorizeHttpRequests(authorize -> authorize
+                .anyRequest().authenticated()
+            )
+            .httpBasic(Customizer.withDefaults())
+            .formLogin(Customizer.withDefaults());
+        return http.build();
+    }
+
+}
+```
+上述代码注册的SecurityFilterChain将拥有如下顺序：
+| Filter | Added by |
+| :-: | :-: |
+| CsrfFilter | HttpSecurity#csrf |
+| UsernamePasswordAuthenticationFilter | HttpSecurity#formLogin |
+| BasicAuthenticationFilter | HttpSecurity#httpBasic |
+| AuthorizationFilter |  HttpSecurity#authorizeHttpRequests | 
+
+> 通常，security filter chain都是先执行authentication再执行authorization
+
+### 自定义Filter
+除了使用Spring Security预置的filter外，还可以使用自定义的filter，自定义filter使用示例如下：
+```java
+// Filter定义
+import java.io.IOException;
+
+import jakarta.servlet.Filter;
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.ServletRequest;
+import jakarta.servlet.ServletResponse;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+
+import org.springframework.security.access.AccessDeniedException;
+
+public class TenantFilter implements Filter {
+
+    @Override
+    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
+        HttpServletRequest request = (HttpServletRequest) servletRequest;
+        HttpServletResponse response = (HttpServletResponse) servletResponse;
+
+        String tenantId = request.getHeader("X-Tenant-Id"); (1)
+        boolean hasAccess = isUserAllowed(tenantId); (2)
+        if (hasAccess) {
+            filterChain.doFilter(request, response); (3)
+            return;
+        }
+        throw new AccessDeniedException("Access denied"); (4)
+    }
+
+}
+```
+```java
+// 将自定义filter添加到SecurityFilterChain中
+@Bean
+SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
+    http
+        // ...
+        .addFilterBefore(new TenantFilter(), AuthorizationFilter.class);
+    return http.build();
+}
+```
+
+
+