spring|spring security中的默认登录页源码跟踪 springsecurity中的默认登录页源码

?2021年的最后2个月，立个flag，要把Spring Security和Spring Security OAuth2的应用及主流程源码研究透彻！
?项目中使用过Spring Security的童鞋都知道，当我们没有单独自定义登录页时，Spring Security自己在初始化的时候会帮我们配置一个默认的登录页，之前一直疑问默认登录页是怎么配置的，今晚特地找了源码跟一下。
springboot项目依赖

org.springframework.bootspring-boot-starter-weborg.springframework.bootspring-boot-starter-security

在项目中随意编写一个接口，然后进行访问

@GetMapping("/")public String hello() {return "hello, spring security"; }

在tomcat默认端口8080，localhost:8080 下访问该接口，spring security会帮我们将路径重定向到默认的登录页

文章图片

?那么这个默认页是怎么来的呢？
原来Spring Security有一个默认的WebSecurityConfigurerAdapter，发现其中有一个init方法，于是在这个方法打了断点，在应用启动的时候进行跟踪。
?跟踪getHttp()方法，this.disableDefaults变量默认为false，意味着将会执行

applyDefaultConfiguration(this.http);

方法。查看applyDefaultConfiguration方法

public void init(WebSecurity web) throws Exception {// 首先配置security要拦截的哪些http请求HttpSecurity http = getHttp(); web.addSecurityFilterChainBuilder(http).postBuildAction(() -> {FilterSecurityInterceptor securityInterceptor = http.getSharedObject(FilterSecurityInterceptor.class); web.securityInterceptor(securityInterceptor); }); }protected final HttpSecurity getHttp() throws Exception {if (this.http != null) {return this.http; }AuthenticationEventPublisher eventPublisher = getAuthenticationEventPublisher(); this.localConfigureAuthenticationBldr.authenticationEventPublisher(eventPublisher); AuthenticationManager authenticationManager = authenticationManager(); this.authenticationBuilder.parentAuthenticationManager(authenticationManager); Map, Object> sharedObjects = createSharedObjects(); this.http = new HttpSecurity(this.objectPostProcessor, this.authenticationBuilder, sharedObjects); if (!this.disableDefaults) {// 默认的配置将会走这个分支applyDefaultConfiguration(this.http); ClassLoader classLoader = this.context.getClassLoader(); List defaultHttpConfigurers = SpringFactoriesLoader.loadFactories(AbstractHttpConfigurer.class, classLoader); for (AbstractHttpConfigurer configurer : defaultHttpConfigurers) {this.http.apply(configurer); }}configure(this.http); return this.http; }

查看applyDefaultConfiguration(this.http)方法，发现http对象new了一个DefaultLoginPageConfigurer对象属性，

private void applyDefaultConfiguration(HttpSecurity http) throws Exception {http.csrf(); http.addFilter(new WebAsyncManagerIntegrationFilter()); http.exceptionHandling(); http.headers(); http.sessionManagement(); http.securityContext(); http.requestCache(); http.anonymous(); http.servletApi(); http.apply(new DefaultLoginPageConfigurer<>()); http.logout(); }

?查看DefaultLoginPageConfigurer类定义，发现它在初始化的同时，它也初始化了自己的2个私有成员变量，分别是DefaultLoginPageGeneratingFilter默认登录页面生成Filter,DefaultLogoutPageGeneratingFilter默认登录页面Filter, 名字起得很好，见名知意，我们马山知道这2个类的含义。
?查看DefaultLoginPageGeneratingFilter的类成员变量，发现定义了一系列跟登录有关的成员变量，包括登录、登录等路径，默认的登录页面路径是"/login"

public class DefaultLoginPageGeneratingFilter extends GenericFilterBean {public static final String DEFAULT_LOGIN_PAGE_URL = "/login"; public static final String ERROR_PARAMETER_NAME = "error"; private String loginPageUrl; private String logoutSuccessUrl; private String failureUrl; private boolean formLoginEnabled; .....

?再结合类名思考，发现是个Filter类，那么它们应该都会重新Filter的doFilter(ServletRequest request, ServletResponse response, FilterChain chain)方法，我们查看一下DefaultLoginPageConfigurer类的``doFilter方法，果然，在doFilter`方法中发现了生成默认登录页面的方法。

private void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain)throws IOException, ServletException {// 判断当前的请求是否被认证通过boolean loginError = isErrorPage(request); boolean logoutSuccess = isLogoutSuccess(request); if (isLoginUrlRequest(request) || loginError || logoutSuccess) {// 当前请求认证失败的话，将会执行这个分支String loginPageHtml = generateLoginPageHtml(request, loginError, logoutSuccess); response.setContentType("text/html; charset=UTF-8"); response.setContentLength(loginPageHtml.getBytes(StandardCharsets.UTF_8).length); response.getWriter().write(loginPageHtml); return; }chain.doFilter(request, response); }private String generateLoginPageHtml(HttpServletRequest request, boolean loginError, boolean logoutSuccess) {String errorMsg = "Invalid credentials"; if (loginError) {HttpSession session = request.getSession(false); if (session != null) {AuthenticationException ex = (AuthenticationException) session.getAttribute(WebAttributes.AUTHENTICATION_EXCEPTION); errorMsg = (ex != null) ? ex.getMessage() : "Invalid credentials"; }}String contextPath = request.getContextPath(); StringBuilder sb = new StringBuilder(); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("Please sign in - 锐客网\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); sb.append("\n"); if (this.formLoginEnabled) {sb.append("
\n"); sb.append("Please sign in\n"); sb.append(createError(loginError, errorMsg) + createLogoutSuccess(logoutSuccess) + "\n"); sb.append("Username\n"); sb.append("\n"); sb.append("
\n"); sb.append("【spring|spring security中的默认登录页源码跟踪】\n"); sb.append("Password\n"); sb.append("\n"); sb.append("
\n"); sb.append(createRememberMe(this.rememberMeParameter) + renderHiddenInputs(request)); sb.append("\n"); sb.append("
\n"); }if (this.openIdEnabled) {sb.append("
\n"); sb.append("Login with OpenID Identity\n"); ......return sb.toString(); }

?我们发现generateLoginPageHtml(HttpServletRequest request, boolean loginError, boolean logoutSuccess)这个方法中使用了最原始的Servlet写html页面的方法，将登录页的html代码写到字符串中写出到前端展示。到这里，我们就大体知道默认登录页面及登出页面是怎么生成的了。
?默认登录页到这里就结束了，有兴趣的可以关注下，接下来会继续写springsecurity的自定义表单认证、授权、会话等内容剖析。距离2022年只剩54天!
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