FormsAuthentication.SignOut() does not log the user out

Jason_38398 0
Viewed 143567

Smashed my head against this a bit too long. How do I prevent a user from browsing a site's pages after they have been logged out using FormsAuthentication.SignOut? I would expect this to do it:

FormsAuthentication.SignOut();
Session.Abandon();
FormsAuthentication.RedirectToLoginPage();

But it doesn't. If I type in a URL directly, I can still browse to the page. I haven't used roll-your-own security in a while so I forget why this doesn't work.

forms-authentication asp.net
23 Answers

Sounds to me like you don't have your web.config authorization section set up properly within . See below for an example.

<authentication mode="Forms">
  <forms name="MyCookie" loginUrl="Login.aspx" protection="All" timeout="90" slidingExpiration="true"></forms>
</authentication>
<authorization>
  <deny users="?" />
</authorization>
jwalkerjr_6890

The key here is that you say "If I type in a URL directly...".

By default under forms authentication the browser caches pages for the user. So, selecting a URL directly from the browsers address box dropdown, or typing it in, MAY get the page from the browser's cache, and never go back to the server to check authentication/authorization. The solution to this is to prevent client-side caching in the Page_Load event of each page, or in the OnLoad() of your base page:

Response.Cache.SetCacheability(HttpCacheability.NoCache);

You might also like to call:

Response.Cache.SetNoStore();
user_18990

The code you posted looks like it should correctly remove the forms authentication token, so it is possible that the folders/pages in question are not actually protected.

Have you confirmed that the pages cannot be accessed before a login has occured?

Can you post the web.config settings and login code that you are using?

AJ_462040

I have been writing a base class for all of my Pages and I came to the same issue. I had code like the following and It didn't work. By tracing, control passes from RedirectToLoginPage() statement to the next line without to be redirected.

if (_requiresAuthentication)
{
    if (!User.Identity.IsAuthenticated)
        FormsAuthentication.RedirectToLoginPage();

    // check authorization for restricted pages only
    if (_isRestrictedPage) AuthorizePageAndButtons();
}

I found out that there are two solutions. Either to modify FormsAuthentication.RedirectToLoginPage(); to be 

if (!User.Identity.IsAuthenticated)
    Response.Redirect(FormsAuthentication.LoginUrl);

OR to modify the web.config by adding

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

In the second case, while tracing, control didn't reach the requested page. It has been redirected immediately to the login url before hitting the break point. Hence, The SignOut() method isn't the issue, the redirect method is the one.

I hope that may help someone

Regards

WaheedS_495080

It could be that you are logging in from one subdomain (sub1.domain.com) and then trying to logout from a different subdomain (www.domain.com).

jorsh1_650050

Are you testing/seeing this behaviour using IE? It's possible that IE is serving up those pages from the cache. It is notoriously hard to get IE to flush it's cache, and so on many occasions, even after you log out, typing the url of one of the "secured" pages would show the cached content from before.

(I've seen this behaviour even when you log as a different user, and IE shows the "Welcome " bar at the top of your page, with the old user's username. Nowadays, usually a reload will update it, but if it's persistant, it could still be a caching issue.)

user_434520
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