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Authentication Cookie not in Request.Cookies

 
 
=?Utf-8?B?Sm9l?=
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Posts: n/a
 
      11-14-2006
In ASP.NET 1.1 I could detected expired form authentication tickets (which
closely coincide with my expired session) by checking for the Authentication
Cookie when the login screen loads. If the cookie exists, then decrypt the
forms auth. ticket and check to see if it is expired. If so display a
message to the user letting them know why they are back on the login screen.
The code I used was something like this:

Dim cookie as HttpCookie =
Request.Cookies(FormsAuthentication.FormsCookieNam e)
Dim ticket as FormsAuthenticationTicket =
FormsAuthentication.Decrypt(cookie.value)
If ticket.IsExpired Then ...

Now when upgrading to ASP.NET 2.0 I am finding that
Request.Cookies(FormsAuthentication.FormsCookieNam e) will only return the
Auth cookie PRIOR to the expiration of the Auth Ticket. Afterwards,
Request.Cookies will not contain the cookie. I can still get to the Cookie
with Request.Headers("Cookie") and manually pull it out but I just wanted to
verify that this is in fact a change in .NET 2.0 and not just me missing
something...Reflector on the HttpRequest.Cookies property doesn't seem to
show anything removing the Auth cookie, so I'm a little perplexed...

Is there a better way to detected expired sessions? I know some people use
the Session.IsNew() property in conjunction with searching for the
preexistance of the session cookie but for me this does not work because I am
dealing with several asp.net apps that share an authentication cookie but all
have different session states. Thus, I just use the auth ticket expiration
as it (used to be) easier to detect...

Thanks in advance for the input!

 
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Walter Wang [MSFT]
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      11-14-2006
Hi,

Based on my understanding, you have two questions:

1) Why the cookie FormsAuthentication.FormsCookieName cannot be found in
Request.Cookies collection after the session is expired in ASP.NET 2.0?

2) What's the recommended way to detect expired sessions?

If I've misunderstood anything, please feel free to let me know.

For question 1), I cannot find documentation on the design change. Also, I
don't think this is the recommended way to detect expired sessions.

For question 2), it's a pity that currently ASP.NET doesn't provide a
built-in way to return this information. Though we do have two commonly
used workarounds:

2.1) The first workaround is create a cookie on Session_OnStart as
described in following FAQ:

#ASP.NET Forums - Understanding session state modes + FAQ
http://forums.asp.net/7504/ShowPost.aspx
Q: How do I detect a session has expired and redirect it to anther page?
A: It's a much requested feature, and unfortunately there is no easy way to
do it right now. We will look into in the next major version. In the
meantime, if you are using cookie, you can store a marker in your cookie so
you can tell the difference between "fresh browser + new session" and "old
browser + expired session". Below is a sample code that will redirect the
page to an expired page if the session has expired.

void Session_OnStart(Object sender, EventArgs e) {
HttpContext context = HttpContext.Current;
HttpCookieCollection cookies = context.Request.Cookies;

if (cookies["starttime"] == null) {
HttpCookie cookie = new HttpCookie("starttime",
DateTime.Now.ToString());
cookie.Path = "/";
context.Response.Cookies.Add(cookie);
}
else {
context.Response.Redirect("expired.aspx");
}
}


2.2) Second workaround is to use the cookie used to store the session id:

#Detecting ASP.NET Session Timeouts: ASP Alliance
http://aspalliance.com/520

if (Context.Session != null)
{
if (Session.IsNewSession)
{
string szCookieHeader = Request.Headers["Cookie"];
if ((null != szCookieHeader) &&
(szCookieHeader.IndexOf("ASP.NET_SessionId") >= 0))
{
Response.Redirect("sessionTimeout.htm");
}
}
}


Additional references:

#Multiple Login Check with Session Ping
http://www.eggheadcafe.com/articles/20040720.asp

#How and why session IDs are reused in ASP.NET
http://support.microsoft.com/kb/899918


Hope this helps. Let me know if you need further information.

Sincerely,
Walter Wang ((E-Mail Removed), remove 'online.')
Microsoft Online Community Support

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