1. 核心类图

   2. 执行登陆  首先请求被拦截器  UsernamePasswordAuthenticationFilter 拦截 看源代码可以看出默认拦截的是  /login 请求地址 当然这个地址是可以被配置的

private static final AntPathRequestMatcher DEFAULT_ANT_PATH_REQUEST_MATCHER = new AntPathRequestMatcher("/login", "POST");

 UsernamePasswordAuthenticationFilter 继承 AbstractAuthenticationProcessingFilter

3.进入AbstractAuthenticationProcessingFilter 的 doFilter

 AbstractAuthenticationProcessingFilter 的核心代码如下  进入

UsernamePasswordAuthenticationFilter.attemptAuthentication()

private void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        if (!this.requiresAuthentication(request, response)) {
            chain.doFilter(request, response);
        } else {
            try {
                //调用了 UsernamePasswordAuthenticationFilter.attemptAuthentication
                Authentication authenticationResult = this.attemptAuthentication(request, response);
                if (authenticationResult == null) {
                    return;
                }

                this.sessionStrategy.onAuthentication(authenticationResult, request, response);
                if (this.continueChainBeforeSuccessfulAuthentication) {
                    chain.doFilter(request, response);
                }

                this.successfulAuthentication(request, response, chain, authenticationResult);
            } catch (InternalAuthenticationServiceException var5) {
                this.logger.error("An internal error occurred while trying to authenticate the user.", var5);
                this.unsuccessfulAuthentication(request, response, var5);
            } catch (AuthenticationException var6) {
                this.unsuccessfulAuthentication(request, response, var6);
            }

        }
    }

UsernamePasswordAuthenticationFilter 的

  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());
        } else {
            String username = this.obtainUsername(request);
            username = username != null ? username.trim() : "";
            String password = this.obtainPassword(request);
            password = password != null ? password : "";
            UsernamePasswordAuthenticationToken authRequest = UsernamePasswordAuthenticationToken.unauthenticated(username, password);
            this.setDetails(request, authRequest);
            return this.getAuthenticationManager().authenticate(authRequest);
        }
    }

这里面有一个走最后一步 交给  AuthenticationManager 去做认证 和类图标识一样  是 

走了 ProviderManager  可以看到以下的源代码 是循环遍历执行认证 

        while(var9.hasNext()) {
            AuthenticationProvider provider = (AuthenticationProvider)var9.next();
            if (provider.supports(toTest)) {
                if (logger.isTraceEnabled()) {
                    Log var10000 = logger;
                    String var10002 = provider.getClass().getSimpleName();
                    ++currentPosition;
                    var10000.trace(LogMessage.format("Authenticating request with %s (%d/%d)", var10002, currentPosition, size));
                }

                try {
                    result = provider.authenticate(authentication);
                    if (result != null) {
                        this.copyDetails(authentication, result);
                        break;
                    }
                } catch (InternalAuthenticationServiceException | AccountStatusException var14) {
                    this.prepareException(var14, authentication);
                    throw var14;
                } catch (AuthenticationException var15) {
                    lastException = var15;
                }
            }
        }

实际上走的是 AbstractUserDetailsAuthenticationProvider  抽象类 有个默认实现 DaoAuthenticationProvider

 user = this.retrieveUser(username, (UsernamePasswordAuthenticationToken)authentication);
            this.preAuthenticationChecks.check(user);
            this.additionalAuthenticationChecks(user, (UsernamePasswordAuthenticationToken)authentication);

additionalAuthenticationChecks 交给 DaoAuthenticationProvider 做验证 和获取用户就是重写了

additionalAuthenticationChecks和 retrieveUser

additionalAuthenticationChecks的代码如下会校验密码对不对：

    protected void additionalAuthenticationChecks(UserDetails userDetails, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException {
        if (authentication.getCredentials() == null) {
            this.logger.debug("Failed to authenticate since no credentials provided");
            throw new BadCredentialsException(this.messages.getMessage("AbstractUserDetailsAuthenticationProvider.badCredentials", "Bad credentials"));
        } else {
            String presentedPassword = authentication.getCredentials().toString();
            if (!this.passwordEncoder.matches(presentedPassword, userDetails.getPassword())) {
                this.logger.debug("Failed to authenticate since password does not match stored value");
                throw new BadCredentialsException(this.messages.getMessage("AbstractUserDetailsAuthenticationProvider.badCredentials", "Bad credentials"));
            }
        }
    }

retrieveUser的代码如下：

    protected final UserDetails retrieveUser(String username, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException {
        this.prepareTimingAttackProtection();

        try {
            UserDetails loadedUser = this.getUserDetailsService().loadUserByUsername(username);
            if (loadedUser == null) {
                throw new InternalAuthenticationServiceException("UserDetailsService returned null, which is an interface contract violation");
            } else {
                return loadedUser;
            }
        } catch (UsernameNotFoundException var4) {
            this.mitigateAgainstTimingAttack(authentication);
            throw var4;
        } catch (InternalAuthenticationServiceException var5) {
            throw var5;
        } catch (Exception var6) {
            throw new InternalAuthenticationServiceException(var6.getMessage(), var6);
        }
    }

调用UserService.locadUserByName 去 查询用户 整合过程有任何不对的都会抛出异常

没有任何异常则 验证通过 这个时候回到 UsernamePasswordAuthenticationFilter 继续执行下面的代码

this.sessionStrategy.onAuthentication(authenticationResult, request, response);
                if (this.continueChainBeforeSuccessfulAuthentication) {
                    chain.doFilter(request, response);
                }

                this.successfulAuthentication(request, response, chain, authenticationResult);

保存session 和 SecurityContextHolder.setContext(context);

再执行 SavedRequestAwareAuthenticationSuccessHandler 的 

    public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) throws ServletException, IOException {
        SavedRequest savedRequest = this.requestCache.getRequest(request, response);
        if (savedRequest == null) {
            super.onAuthenticationSuccess(request, response, authentication);
        } else {
            String targetUrlParameter = this.getTargetUrlParameter();
            if (!this.isAlwaysUseDefaultTargetUrl() && (targetUrlParameter == null || !StringUtils.hasText(request.getParameter(targetUrlParameter)))) {
                this.clearAuthenticationAttributes(request);
                String targetUrl = savedRequest.getRedirectUrl();
                this.getRedirectStrategy().sendRedirect(request, response, targetUrl);
            } else {
                this.requestCache.removeRequest(request, response);
                super.onAuthenticationSuccess(request, response, authentication);
            }
        }
    }

做重定向