.NET PASSPORT

1. A client issues an HTTP GET request for a protected resource, such as http://www.contoso.com/default.aspx.
2. The client's cookies are examined for an existing Passport authentication ticket. If the site finds valid credentials, the site authenticates the client. If the request does not include a valid authentication ticket, the server returns status code 302 and redirects the client to the Passport Logon Service. The response includes a URL in the query string that is sent to the Passport logon service to direct the client back to the original site.
3. The client follows the redirect, issues an HTTP GET request to the Passport logon server, and transmits the query string information from the original site.
4. The Passport logon server presents the client with a logon form.
5. The client fills out the form and does a POST back to the logon server, using Secure Sockets Layer (SSL).
6. The logon server authenticates the user and redirects the client back to the original URL (http://www.contoso.com/default.aspx). The response contains an encrypted Passport cookie in the query string.
7. The client follows the redirect and requests the original protected resource again, this time with the Passport cookie.
8. Back on the originating server, the PassportAuthenticationModule detects the presence of the Passport cookie and tests for authentication. If successful, the request is then authenticated.

Here are few more links

http://technet.microsoft.com/en-us/library/cc778966(WS.10).aspx

Set Up passport authentication

http://www.devx.com/security/Article/17483

Implement passport authentication

http://www.techrepublic.com/article/integrate-passport-authentication-into-your-aspnet-applications/1052982

I suggest you to implement single sign-on using forms authentication without involving the passport SDK

Single sign-on (SSO) is a specialized form of software authentication that enables a user to authenticate once and gain access to the resources of multiple software systems

http://weblogs.asp.net/hernandl/archive/2004/06/09/ssoformsauth.aspx

Hope this helps