Spring|Spring Security登陆流程讲解 SpringSecurity登陆流程讲解

在Spring Security中，认证授权都是通过过滤器来实现的。
当开始登陆的时候，有一个关键的过滤器UsernamePasswordAuthenticationFilter，该类继承抽象类AbstractAuthenticationProcessingFilter，在AbstractAuthenticationProcessingFilter里有一个doFilter方法，一切先从这里说起。

private void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain)throws IOException, ServletException {if (!requiresAuthentication(request, response)) {chain.doFilter(request, response); return; }try {Authentication authenticationResult = attemptAuthentication(request, response); if (authenticationResult == null) {// return immediately as subclass has indicated that it hasn't completedreturn; }this.sessionStrategy.onAuthentication(authenticationResult, request, response); // Authentication successif (this.continueChainBeforeSuccessfulAuthentication) {chain.doFilter(request, response); }successfulAuthentication(request, response, chain, authenticationResult); }catch (InternalAuthenticationServiceException failed) {this.logger.error("An internal error occurred while trying to authenticate the user.", failed); unsuccessfulAuthentication(request, response, failed); }catch (AuthenticationException ex) {// Authentication failedunsuccessfulAuthentication(request, response, ex); }}

首先requiresAuthentication先判断是否尝试校验，通过后调用attemptAuthentication方法，这个方法也就是UsernamePasswordAuthenticationFilter 中的attemptAuthentication方法。

public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response)throws AuthenticationException {if (this.postOnly && !request.getMethod().equals("POST")) {throw new AuthenticationServiceException("Authentication method not supported: " + request.getMethod()); }String username = obtainUsername(request); username = (username != null) ? username : ""; username = username.trim(); String password = obtainPassword(request); password = (password != null) ? password : ""; UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(username, password); // Allow subclasses to set the "details" propertysetDetails(request, authRequest); return this.getAuthenticationManager().authenticate(authRequest); }

1.在UsernamePasswordAuthenticationFilter 的attemptAuthentication方法中，先是验证请求的类型，是否是POST请求，如果不是的话，抛出异常。(PS：登陆肯定要用POST方法了)
2.然后拿到username和password。这里使用的是obtainUsername方法，也就是get方法。

@Nullableprotected String obtainPassword(HttpServletRequest request) {return request.getParameter(this.passwordParameter); }@Nullableprotected String obtainUsername(HttpServletRequest request) {return request.getParameter(this.usernameParameter); }

由此我们知道了Spring Security中是通过get方法来拿到参数，所以在进行前后端分离的时候是无法接受JSON数据，处理方法就是自定义一个Filter来继承UsernamePasswordAuthenticationFilter，重写attemptAuthentication方法，然后创建一个Filter实例写好登陆成功和失败的逻辑处理，在HttpSecurity参数的configure中通过addFilterAt来替换Spring Security官方提供的过滤器。
3.创建一个UsernamePasswordAuthenticationToken 实例。
4.设置Details，在这里关键的是在WebAuthenticationDetails类中记录了用户的remoteAddress和sessionId。

public WebAuthenticationDetails(HttpServletRequest request) {this.remoteAddress = request.getRemoteAddr(); HttpSession session = request.getSession(false); this.sessionId = (session != null) ? session.getId() : null; }

5.拿到一个AuthenticationManager通过authenticate方法进行校验，这里以实现类ProviderManager为例。

@Overridepublic Authentication authenticate(Authentication authentication) throws AuthenticationException {//获取Authentication的运行时类Class toTest = authentication.getClass(); AuthenticationException lastException = null; AuthenticationException parentException = null; Authentication result = null; Authentication parentResult = null; int currentPosition = 0; int size = this.providers.size(); for (AuthenticationProvider provider : getProviders()) {//判断是否支持处理该类别的providerif (!provider.supports(toTest)) {continue; }if (logger.isTraceEnabled()) {logger.trace(LogMessage.format("Authenticating request with %s (%d/%d)",provider.getClass().getSimpleName(), ++currentPosition, size)); }try {//获取用户的信息result = provider.authenticate(authentication); if (result != null) {copyDetails(authentication, result); break; }}catch (AccountStatusException | InternalAuthenticationServiceException ex) {prepareException(ex, authentication); // SEC-546: Avoid polling additional providers if auth failure is due to// invalid account statusthrow ex; }catch (AuthenticationException ex) {lastException = ex; }}//不支持的话跳出循环再次执行if (result == null && this.parent != null) {// Allow the parent to try.try {parentResult = this.parent.authenticate(authentication); result = parentResult; }catch (ProviderNotFoundException ex) {// ignore as we will throw below if no other exception occurred prior to// calling parent and the parent// may throw ProviderNotFound even though a provider in the child already// handled the request}catch (AuthenticationException ex) {parentException = ex; lastException = ex; }}if (result != null) {//擦除用户的凭证也就是密码if (this.eraseCredentialsAfterAuthentication && (result instanceof CredentialsContainer)) {// Authentication is complete. Remove credentials and other secret data// from authentication((CredentialsContainer) result).eraseCredentials(); }// If the parent AuthenticationManager was attempted and successful then it// will publish an AuthenticationSuccessEvent// This check prevents a duplicate AuthenticationSuccessEvent if the parent// AuthenticationManager already published itif (parentResult == null) {//公示登陆成功this.eventPublisher.publishAuthenticationSuccess(result); }return result; }// Parent was null, or didn't authenticate (or throw an exception).if (lastException == null) {lastException = new ProviderNotFoundException(this.messages.getMessage("ProviderManager.providerNotFound",new Object[] { toTest.getName() }, "No AuthenticationProvider found for {0}")); }// If the parent AuthenticationManager was attempted and failed then it will// publish an AbstractAuthenticationFailureEvent// This check prevents a duplicate AbstractAuthenticationFailureEvent if the// parent AuthenticationManager already published itif (parentException == null) {prepareException(lastException, authentication); }throw lastException; }

6.经过一系列校验，此时登陆校验基本完成，当验证通过后会执行doFilter中的successfulAuthentication方法，跳转到我们设置的登陆成功界面，验证失败会执行unsuccessfulAuthentication方法，跳转到我们设置的登陆失败界面。

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