ASP.NET Tip: Persistent Logins Under ASP.NET 2.0

For some sites, allowing users to "save their passwords" is not a major security concern, and it speeds up the user's ability to interact with the site. Assuming your site security can allow for persistent logins, this feature also is easy to provide. Under ASP.NET 1.x, the built-in FormsAuthentication enabled this very easily: it simply specified a True argument when the user ID was saved using FormsAuthentication.RedirectFromLoginPage.

However, ASP.NET 2.0 has changed how the forms authentication tickets work. Simply using the same method with a True argument won't actually persist the cookie. If you want to have a significantly longer timeout for your forms authentication ticket, the code in this tip performs the same steps as the built-in FormsAuthentication methods but gives you more control over the specifics of how it works.

For starters, you'll need to add a block to your Web.config to enable FormsAuthentication:

<authentication mode="Forms">
   <forms name="MyApplication" loginUrl="/login.aspx" />
</authentication>

If you want to switch into SSL mode for the login, you can specify the full URL, including the "https://" prefix in the loginUrl parameter. Also add an authorization section to lock down your entire site or virtual directory:

<authorization>
   <deny users="?"/>
</authorization>

The code in your login form, after you've done your own validation to see if the user can log into your application, looks like this:

FormsAuthenticationTicket t =
   new FormsAuthenticationTicket(1, userID,
      DateTime.Now, DateTime.Now.AddMonths(3),
      chkSave.Checked, userID.ToString(),
       FormsAuthentication.FormsCookiePath);

string encTicket = FormsAuthentication.Encrypt(t);

HttpCookie c = new HttpCookie(FormsAuthentication.FormsCookieName,
                              encTicket);

if (chkSave.Checked)
   c.Expires = DateTime.Now.AddMonths(3);

Response.Cookies.Add(c);

In this example, the userID variable is the value that will be available if you look at User.Identity.Name after the user has logged in. On my page, chkSave is a check box that lets the user indicate whether or not to save the password. That true/false value is passed into the FormsAuthenticationTicket constructor to mark the ticket as persistent or not. After you get the ticket back, encrypt it and then put it into the designated cookie.

If the user has chosen to save the cookie, the cookie needs to be assigned an expiration date. In this case, I'm using three months as the expiration timeframe.

About the Author

Eric Smith is the owner of Northstar Computer Systems, a Web-hosting company based in Indianapolis, Indiana. He is also a MCT and MCSD who has been developing with .NET since 2001. In addition, he has written or contributed to 12 books covering .NET, ASP, and Visual Basic. Send him your questions and feedback via e-mail at questions@techniquescentral.com.



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