mvc中DotNetOpenAuth实现了第三方应用访问自己的网站

以yahoo为例吧，即从yahoo取得用户信息，存到自己的站点，实现了用户信息在一次录入多处共享的功能。
以下是在点击了使用yahoo登录本站的链接后执行action:OpenId.          
ProviderUrl="http://yahoo.com"
Action OpenId会被执行两次，一次是自己的站点请求的，此时response==null;一次是yahoo请求的,response!=null.

using DotNetOpenAuth.OpenId;
using DotNetOpenAuth.OpenId.RelyingParty;
using DotNetOpenAuth.OpenId.Provider;
using DotNetOpenAuth.OpenId.Extensions.AttributeExchange;
using DotNetOpenAuth.Messaging;

static private readonly OpenIdRelyingParty Openid = new OpenIdRelyingParty();//一个重要的类
 public ActionResult OpenId(string ProviderUrl)
        {
            FormsAuthentication auth = new FormsAuthentication();
            var response = Openid.GetResponse();
            if (response == null)//自己站点的请求
            {
                Identifier id;
                if (Identifier.TryParse(ProviderUrl, out id))//第三方网站地址能产生一个有效标识符时
                {
                    var request = Openid.CreateRequest(id);
                    var fetch = new FetchRequest();//定义在这次请求中都想要获取到用户的哪些信息
                    fetch.Attributes.AddRequired(WellKnownAttributes.Name.First);
                    fetch.Attributes.AddRequired(WellKnownAttributes.Name.Last);
                    fetch.Attributes.AddRequired(WellKnownAttributes.Contact.Email);
                    request.AddExtension(fetch);
                    return request.RedirectingResponse.AsActionResult();//页面跳转到了yahoo
                }
                return RedirectToAction("Index");
            }
            switch (response.Status)//yahoo登录后，返回到自己的站点时，根据不用的response status来做不同的处理
            {
                case AuthenticationStatus.Authenticated:
                    var fetch = response.GetExtension<FetchResponse>();
                    string firstName = string.Empty;
                    string lastName = string.Empty;
                    string email = string.Empty;
                    if (fetch != null)
                    {
                        firstName = fetch.GetAttributeValue(WellKnownAttributes.Name.First);
                        lastName = fetch.GetAttributeValue(WellKnownAttributes.Name.Last);
                        email = fetch.GetAttributeValue(WellKnownAttributes.Contact.Email);
                    }

　　　　　　　　　　   return CreateUser(response.ClaimedIdentifier, firstName, lastName, email);//可以将用户的信息存入到自己的数据库

                case AuthenticationStatus.Failed:
                    return RedirectToAction("Index");

                default:
                    return RedirectToAction("Index");

            }
        }

dotNetOpenAuth也可以实现sso,只是觉得晦涩难懂。比如：

<?xml version="1.0" encoding="UTF-8"?>
<xrds:XRDS
    xmlns:xrds="xri://$xrds"
    xmlns:openid="http://openid.net/xmlns/1.0"
    xmlns="xri://$xrd*($v*2.0)">
    <XRD>
        <Service priority="">
            <Type>http://specs.openid.net/auth/2.0/signon</Type>
            <Type>http://openid.net/extensions/sreg/1.1</Type>
            <URI>@uri1</URI>
        </Service>
        <Service priority="">
            <Type>http://openid.net/signon/1.0</Type>
            <Type>http://openid.net/extensions/sreg/1.1</Type>
            <URI>@uri2</URI>
        </Service>
    </XRD>
</xrds:XRDS>

这里边具体都是做什么用呢，也找不到资料，觉得用dotnetopenauth实现sso可能有点自找麻烦的感觉。有对这块熟悉的吗？