流程分析：
1、 请求/hello接口，在引入springsecurity之后会先经过一些列过滤器；
2、 在请求到达FilterSecurityInterceptor时，发现请求并未认证请求拦截下来，并抛出AccessDeniedException异常；
3. 抛出 AccessDeniedException 的异常会被 ExceptionTranslationFilter 捕获，这个 Filter 中会调用 LoginUrlAuthenticationEntryPoint#commence方法给客户端返回 302，要求客户端进行重定向到 /login ⻚面。
4、 客户端发送/login请求；
5、 /login请求会再次被拦截器中DefaultLoginPageGeneratingFilter拦截到，并在拦截器中返回生成登录⻚面；
如何生成默认登录页面？进入 DefaultLoginPageGeneratingFilter 源码：
public class DefaultLoginPageGeneratingFilter extends GenericFilterBean {
private void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
throws IOException, ServletException {
boolean loginError = isErrorPage(request);
boolean logoutSuccess = isLogoutSuccess(request);
if (isLoginUrlRequest(request) || loginError || logoutSuccess) {
// 生成登录页面
String loginPageHtml = generateLoginPageHtml(request, loginError, logoutSuccess);
response.setContentType("text/html;charset=UTF-8");
response.setContentLength(loginPageHtml.getBytes(StandardCharsets.UTF_8).length);
// 将登录页面响应给客户端
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();
// 登录页面：拼接前端登录页面字符串
StringBuilder sb = new StringBuilder();
sb.append("<!DOCTYPE html>\n");
sb.append("<html lang=\"en\">\n");
sb.append(" <head>\n");
sb.append(" <meta charset=\"utf-8\">\n");
sb.append(" <meta name=\"viewport\" content=\"width=device-width, initial-scale=1, shrink-to-fit=no\">\n");
sb.append(" <meta name=\"description\" content=\"\">\n");
sb.append(" <meta name=\"author\" content=\"\">\n");
sb.append(" <title>Please sign in</title>\n");
sb.append(" <link href=\"https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css\" "
+ "rel=\"stylesheet\" integrity=\"sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M\" crossorigin=\"anonymous\">\n");
sb.append(" <link href=\"https://getbootstrap.com/docs/4.0/examples/signin/signin.css\" "
+ "rel=\"stylesheet\" crossorigin=\"anonymous\"/>\n");
sb.append(" </head>\n");
sb.append(" <body>\n");
sb.append(" <div class=\"container\">\n");
if (this.formLoginEnabled) {
sb.append(" <form class=\"form-signin\" method=\"post\" action=\"" + contextPath
+ this.authenticationUrl + "\">\n");
sb.append(" <h2 class=\"form-signin-heading\">Please sign in</h2>\n");
sb.append(createError(loginError, errorMsg) + createLogoutSuccess(logoutSuccess) + " <p>\n");
sb.append(" <label for=\"username\" class=\"sr-only\">Username</label>\n");
sb.append(" <input type=\"text\" id=\"username\" name=\"" + this.usernameParameter
+ "\" class=\"form-control\" placeholder=\"Username\" required autofocus>\n");
sb.append(" </p>\n");
sb.append(" <p>\n");
sb.append(" <label for=\"password\" class=\"sr-only\">Password</label>\n");
sb.append(" <input type=\"password\" id=\"password\" name=\"" + this.passwordParameter
+ "\" class=\"form-control\" placeholder=\"Password\" required>\n");
sb.append(" </p>\n");
sb.append(createRememberMe(this.rememberMeParameter) + renderHiddenInputs(request));
sb.append(" <button class=\"btn btn-lg btn-primary btn-block\" type=\"submit\">Sign in</button>\n");
sb.append(" </form>\n");
}
if (this.openIdEnabled) {
sb.append(" <form name=\"oidf\" class=\"form-signin\" method=\"post\" action=\"" + contextPath
+ this.openIDauthenticationUrl + "\">\n");
sb.append(" <h2 class=\"form-signin-heading\">Login with OpenID Identity</h2>\n");
sb.append(createError(loginError, errorMsg) + createLogoutSuccess(logoutSuccess) + " <p>\n");
sb.append(" <label for=\"username\" class=\"sr-only\">Identity</label>\n");
sb.append(" <input type=\"text\" id=\"username\" name=\"" + this.openIDusernameParameter
+ "\" class=\"form-control\" placeholder=\"Username\" required autofocus>\n");
sb.append(" </p>\n");
sb.append(createRememberMe(this.openIDrememberMeParameter) + renderHiddenInputs(request));
sb.append(" <button class=\"btn btn-lg btn-primary btn-block\" type=\"submit\">Sign in</button>\n");
sb.append(" </form>\n");
}
if (this.oauth2LoginEnabled) {
sb.append("<h2 class=\"form-signin-heading\">Login with OAuth 2.0</h2>");
sb.append(createError(loginError, errorMsg));
sb.append(createLogoutSuccess(logoutSuccess));
sb.append("<table class=\"table table-striped\">\n");
for (Map.Entry<String, String> clientAuthenticationUrlToClientName : this.oauth2AuthenticationUrlToClientName
.entrySet()) {
sb.append(" <tr><td>");
String url = clientAuthenticationUrlToClientName.getKey();
sb.append("<a href=\"").append(contextPath).append(url).append("\">");
String clientName = HtmlUtils.htmlEscape(clientAuthenticationUrlToClientName.getValue());
sb.append(clientName);
sb.append("</a>");
sb.append("</td></tr>\n");
}
sb.append("</table>\n");
}
if (this.saml2LoginEnabled) {
sb.append("<h2 class=\"form-signin-heading\">Login with SAML 2.0</h2>");
sb.append(createError(loginError, errorMsg));
sb.append(createLogoutSuccess(logoutSuccess));
sb.append("<table class=\"table table-striped\">\n");
for (Map.Entry<String, String> relyingPartyUrlToName : this.saml2AuthenticationUrlToProviderName
.entrySet()) {
sb.append(" <tr><td>");
String url = relyingPartyUrlToName.getKey();
sb.append("<a href=\"").append(contextPath).append(url).append("\">");
String partyName = HtmlUtils.htmlEscape(relyingPartyUrlToName.getValue());
sb.append(partyName);
sb.append("</a>");
sb.append("</td></tr>\n");
}
sb.append("</table>\n");
}
sb.append("</div>\n");
sb.append("</body></html>");
return sb.toString();
}
}
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