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前后端分离模式是指由前端控制页面路由，后端接口也不再返回html数据，而是直接返回业务数据，数据一般是JSON格式。Spring Security默认的表单登录方式，在未登录或登录成功时会发起页面重定向，在提交登录数据时，也不是JSON格式。要支持前后端分离模式，要对这些问题进行改造。

1. 认证信息改成JSON格式

Spring Security默认提供账号密码认证方式，具体实现是在UsernamePasswordAuthenticationFilter 中。因为是表单提交，所以Filter中用request.getParameter(this.usernameParameter) 来获取用户信息。当我们将数据改成JSON，并放入HTTP Body后，getParameter 就没法获取到信息。

要解决这个问题，就要新建Filter来替换UsernamePasswordAuthenticationFilter ，然后覆盖掉获取用户的方法。

1.1 新建JsonUsernamePasswordAuthenticationFilter

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.SneakyThrows;
import org.springframework.data.util.Pair;
import org.springframework.security.authentication.AuthenticationServiceException;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.AuthenticationException;
import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;public class JsonUsernamePasswordAuthenticationFilter extends UsernamePasswordAuthenticationFilter {@Overridepublic Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response)throws AuthenticationException {if (!request.getMethod().equals("POST")) {throw new AuthenticationServiceException("Authentication method not supported: " + request.getMethod());}Pair<String, String> usernameAndPassword = obtainUsernameAndPassword(request);String username = usernameAndPassword.getFirst();username = (username != null) ? username.trim() : "";String password = usernameAndPassword.getSecond();password = (password != null) ? password : "";UsernamePasswordAuthenticationToken authRequest = UsernamePasswordAuthenticationToken.unauthenticated(username,password);// Allow subclasses to set the "details" propertysetDetails(request, authRequest);return this.getAuthenticationManager().authenticate(authRequest);}@SneakyThrowsprivate Pair<String, String> obtainUsernameAndPassword(HttpServletRequest request) {JSONObject map = JSON.parseObject(request.getInputStream(), JSONObject.class);return Pair.of(map.getString(getUsernameParameter()), map.getString(getPasswordParameter()));}
}

1.2 新建JsonUsernamePasswordLoginConfigurer

注册Filter有两种方式，一给是直接调用httpSecurity的addFilterAt(Filter filter, Class<? extends Filter> atFilter) ，另一个是注册通过AbstractHttpConfigurer 来注册。我们选择第二种方式来注册Filter，因为AbstractHttpConfigurer 在初始化 UsernamePasswordAuthenticationFilter 的时候，会额外设置一些信息。新建一个自己的AbstractHttpConfigurer

import org.springframework.security.config.annotation.web.HttpSecurityBuilder;
import org.springframework.security.config.annotation.web.configurers.AbstractAuthenticationFilterConfigurer;
import org.springframework.security.web.util.matcher.AntPathRequestMatcher;
import org.springframework.security.web.util.matcher.RequestMatcher;public final class JsonUsernamePasswordLoginConfigurer<H extends HttpSecurityBuilder<H>> extendsAbstractAuthenticationFilterConfigurer<H, JsonUsernamePasswordLoginConfigurer<H>, JsonUsernamePasswordAuthenticationFilter> {public JsonUsernamePasswordLoginConfigurer() {super(new JsonUsernamePasswordAuthenticationFilter(), null);}@Overrideprotected RequestMatcher createLoginProcessingUrlMatcher(String loginProcessingUrl) {return new AntPathRequestMatcher(loginProcessingUrl, "POST");}
}

1.3 注册JJsonUsernamePasswordLoginConfigurer到HttpSecurity

这一步比较简单，直接关闭表单登录，然后注册我们自己的Filter。

http.formLogin().disable().apply(new JsonUsernamePasswordLoginConfigurer<>())

经过这三步，Spring Security就能识别JSON格式的用户信息。

2. 去掉重定向

有几个场景会触发Spring Security的重定向：

1. 未登录，重定向到登录页面

2. 登录验证成功，重定向到默认页面

3. 退出登录，重定向到默认页面

我们要对这几个场景分别处理，给前端返回错误信息，而不是重定向。

2.1 未登录请求

未登录的请求会被AuthorizationFilter拦截，并抛出异常。异常被AuthenticationEntryPoint处理，默认会触发重定向到登录页。我们通过自定义AuthenticationEntryPoint来取消重定向行为，改为返回JSON信息。

http
// 1. 未登录的请求会被AuthorizationFilter拦截，并抛出异常。
.exceptionHandling(it -> it.authenticationEntryPoint((request, response, authException) -> {log.info("get exception {}", authException.getClass());String msg = "{\\"msg\\": \\"用户未登录\\"}";response.setStatus(HttpStatus.FORBIDDEN.value());response.setContentType(MediaType.APPLICATION_JSON_VALUE);PrintWriter writer = response.getWriter();writer.write(msg);writer.flush();writer.close();
}))

2.2 登录成功/失败

登录成功或失败后的行为由AuthenticationSuccessHandler 和AuthenticationFailureHandler 来控制。由于上面我们自定义了JsonUsernamePasswordLoginConfigurer ，所以要配置自定义Configurer 上的AuthenticationSuccessHandler 和AuthenticationFailureHandler 。

http.formLogin().disable().apply((SecurityConfigurerAdapter) new JsonUsernamePasswordLoginConfigurer<>().successHandler((request, response, authentication) -> {String msg = "{\\"msg\\": \\"登录成功\\"}";response.setStatus(HttpStatus.OK.value());response.setContentType(MediaType.APPLICATION_JSON_VALUE);PrintWriter writer = response.getWriter();writer.write(msg);writer.flush();writer.close();}).failureHandler((request, response, exception) -> {String msg = "{\\"msg\\": \\"用户名密码错误\\"}";response.setStatus(HttpStatus.UNAUTHORIZED.value());response.setContentType(MediaType.APPLICATION_JSON_VALUE);PrintWriter writer = response.getWriter();writer.write(msg);writer.flush();writer.close();}));

2.3 退出登录

// 退出登录
.logout(it -> it.logoutSuccessHandler((request, response, authentication) -> {String msg = "{\\"msg\\": \\"退出成功\\"}";response.setStatus(HttpStatus.OK.value());response.setContentType(MediaType.APPLICATION_JSON_VALUE);PrintWriter writer = response.getWriter();writer.write(msg);writer.flush();writer.close();}))

3. 最后处理CSRF校验

由于前端直接调用登录接口，跳过了获取登录页面的步骤，所以服务端没有机会将CSRF Token传给前段，所以要把POST /login接口的CSRF校验剔除掉。

http.csrf(it -> it.ignoringRequestMatchers("/login", "POST"))