自定义HttpModule，用于未登录用户，不弹出Windows认证窗口，而是跳转回SSO站点

2012年的一篇随笔记录，可以学习到如何自定义HttpModule，而具体里面针对需求开发的代码，可能未必能让大伙了解到什么，可快速扫描而过。

using System;
using System.Web;
 
using System.Configuration;
using System.Web.Configuration;
using Microsoft.SharePoint;
using System.Net;
using System.Security.Principal;
 
namespace WebApplication1.EventHandlers
{
    /// <summary>
    /// Windows认证下实现URL重定向，如:
    /// 1、未登录用户，不弹出Windows认证窗口，而是跳转回SSO站点；
    /// 2、支持SharePoint匿名站点，暂时不支持文档库或列表库断开继承后匿名访问的情况
    /// </summary>
    public class SSORedirect : IHttpModule
    {
        public void Dispose()
        {
            //throw new NotImplementedException();
        }
 
        public void Init(HttpApplication context)
        {
            context.AuthenticateRequest += new EventHandler(context_AuthenticateRequest);
        }
 
        /// <summary>
        /// 当ASP.NET 运行时准备验证用户身份的时候引发这个事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        internal void context_AuthenticateRequest(object sender, EventArgs e)
        {
            try
            {
                // 忽略POSTBack的请求
                HttpContext context = HttpContext.Current;
                if (context == null || context.Request.HttpMethod.ToUpper() == "POST")
                {
                    return;
                }
 
                if (IsWindowsAuth())
                {
                    string url = context.Request.Url.AbsolutePath.ToString().ToLower();//"/"
                    string fullUrl = context.Request.Url.OriginalString.ToString().ToLower();//"http://yxjt.contoso.com:80/"
 
                    string strSSOUrl = "/Test/Default.aspx";//ConfigurationManager.AppSettings["SSOUrl"];
                    if (!string.IsNullOrEmpty(strSSOUrl))
                    {
                        if (url.IndexOf(strSSOUrl.ToLower()) == -1)
                        {
                            if (!IsAnonymous(fullUrl))//是否为非匿名访问的页面
                            {
                                if (!context.Request.IsAuthenticated && IsValidUrl(url))//是否为未登录用户，并且是需验证的有效的地址
                                {
                                    context.Response.Redirect(strSSOUrl);
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
 
            }
        }
 
        /// <summary>
        /// 判断是否为Windows认证
        /// </summary>
        /// <returns>是否为Windows认证</returns>
        private bool IsWindowsAuth()
        {
            Configuration c = WebConfigurationManager.OpenWebConfiguration("/web.config");
            AuthenticationSection auth = (AuthenticationSection)c.GetSection("system.web/authentication");
            return auth.Mode == AuthenticationMode.Windows;
        }
 
        /// <summary>
        /// 判断是否为允许匿名访问的站点
        /// </summary>
        /// <param name="requestFullUrl">请求的地址，例如"http://yxjt.contoso.com:80/"</param>
        /// <returns>是否为允许匿名访问的站点</returns>
        private bool IsAnonymous(string requestFullUrl)
        {
            bool isAnonymous = false;
            requestFullUrl = requestFullUrl.Split(new char[] { '?' })[0];
 
            SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                SPSite site = new SPSite(requestFullUrl);//这里不要用using自动垃圾回收，否则抛异常
                SPWeb web = site.OpenWeb();//关键写法
                isAnonymous = web.AllowAnonymousAccess;
            });
            return isAnonymous;
        }
 
        /// <summary>
        /// 判断是否是有效的地址
        /// </summary>
        /// <param name="requestUrl">请求的地址，例如"/"</param>
        /// <returns>是否是有效的地址</returns>
        private bool IsValidUrl(string requestUrl)
        {
            bool isValidUrl = false;
            requestUrl = requestUrl.Split(new char[] { '?' })[0];
            int index = requestUrl.LastIndexOf(".");
            if (index != -1)//是否包含.号
            {
                isValidUrl = requestUrl.EndsWith(".aspx");//是否以.aspx结尾的url
            }
            else
            {
                isValidUrl = true;
            }
            return isValidUrl;
        }
    }
}