Related
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.
Users can still browse your website because cookies are not cleared when you call FormsAuthentication.SignOut() and they are authenticated on every new request. In MS documentation is says that cookie will be cleared but they don't, bug?
Its exactly the same with Session.Abandon(), cookie is still there.
You should change your code to this:
FormsAuthentication.SignOut();
Session.Abandon();
// clear authentication cookie
HttpCookie cookie1 = new HttpCookie(FormsAuthentication.FormsCookieName, "");
cookie1.Expires = DateTime.Now.AddYears(-1);
Response.Cookies.Add(cookie1);
// clear session cookie (not necessary for your current problem but i would recommend you do it anyway)
SessionStateSection sessionStateSection = (SessionStateSection)WebConfigurationManager.GetSection("system.web/sessionState");
HttpCookie cookie2 = new HttpCookie(sessionStateSection.CookieName, "");
cookie2.Expires = DateTime.Now.AddYears(-1);
Response.Cookies.Add(cookie2);
FormsAuthentication.RedirectToLoginPage();
HttpCookie is in the System.Web namespace. MSDN Reference.
Using two of the above postings by x64igor and Phil Haselden solved this:
1. x64igor gave the example to do the Logout:
You first need to Clear the Authentication Cookie and Session Cookie by passing back empty cookies in the Response to the Logout.
public ActionResult LogOff()
{
FormsAuthentication.SignOut();
Session.Clear(); // This may not be needed -- but can't hurt
Session.Abandon();
// Clear authentication cookie
HttpCookie rFormsCookie = new HttpCookie( FormsAuthentication.FormsCookieName, "" );
rFormsCookie.Expires = DateTime.Now.AddYears( -1 );
Response.Cookies.Add( rFormsCookie );
// Clear session cookie
HttpCookie rSessionCookie = new HttpCookie( "ASP.NET_SessionId", "" );
rSessionCookie.Expires = DateTime.Now.AddYears( -1 );
Response.Cookies.Add( rSessionCookie );
2. Phil Haselden gave the example above of how to prevent caching after logout:
You need to Invalidate the Cache on the Client Side via the Response.
// Invalidate the Cache on the Client Side
Response.Cache.SetCacheability( HttpCacheability.NoCache );
Response.Cache.SetNoStore();
// Redirect to the Home Page (that should be intercepted and redirected to the Login Page first)
return RedirectToAction( "Index", "Home" );
}
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>
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();
I've struggled with this before too.
Here's an analogy for what seems to be going on... A new visitor, Joe, comes to the site and logs in via the login page using FormsAuthentication. ASP.NET generates a new identity for Joe, and gives him a cookie. That cookie is like the key to the house, and as long as Joe returns with that key, he can open the lock. Each visitor is given a new key and a new lock to use.
When FormsAuthentication.SignOut() is called, the system tells Joe to lose the key. Normally, this works, since Joe no longer has the key, he cannot get in.
However, if Joe ever comes back, and does have that lost key, he is let back in!
From what I can tell, there is no way to tell ASP.NET to change the lock on the door!
The way I can live with this is to remember Joe's name in a Session variable. When he logs out, I abandon the Session so I don't have his name anymore. Later, to check if he is allowed in, I simply compare his Identity.Name to what the current session has, and if they don't match, he is not a valid visitor.
In short, for a web site, do NOT rely on User.Identity.IsAuthenticated without also checking your Session variables!
After lots of search finally this worked for me . I hope it helps.
public ActionResult LogOff()
{
AuthenticationManager.SignOut();
HttpContext.User = new GenericPrincipal(new GenericIdentity(string.Empty), null);
return RedirectToAction("Index", "Home");
}
<li class="page-scroll">#Html.ActionLink("Log off", "LogOff", "Account")</li>
This works for me
public virtual ActionResult LogOff()
{
FormsAuthentication.SignOut();
foreach (var cookie in Request.Cookies.AllKeys)
{
Request.Cookies.Remove(cookie);
}
foreach (var cookie in Response.Cookies.AllKeys)
{
Response.Cookies.Remove(cookie);
}
return RedirectToAction(MVC.Home.Index());
}
This Answer is technically identical to Khosro.Pakmanesh. I'm posting it to clarify how his answer differs from other answers on this thread, and in which use case it can be used.
In general to clear a user-session, doing
HttpContext.Session.Abandon();
FormsAuthentication.SignOut();
will effectively log out the user. However, if in the same Request you need to check Request.isAuthenticated (as may often happen in an Authorization Filter, for example), then you will find that
Request.isAuthenticated == true
even _after you did HttpContext.Session.Abandon() and FormsAuthentication.SignOut().
The only thing that worked was doing
AuthenticationManager.SignOut();
HttpContext.User = new GenericPrincipal(new GenericIdentity(string.Empty), null);
That effectively sets Request.isAuthenticated = false.
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?
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
I just tried some of the suggestions here and while I was able to use the browser back button, when I clicked on a menu selection the [Authorize] token for that [ActionResult] sent me right back to the login screen.
Here is my logout code:
FormsAuthentication.SignOut();
Response.Cookies.Remove(FormsAuthentication.FormsCookieName);
Response.Cache.SetExpires(DateTime.Now.AddSeconds(-1));
HttpCookie cookie = HttpContext.Request.Cookies[FormsAuthentication.FormsCookieName];
if (cookie != null)
{
cookie.Expires = DateTime.Now.AddDays(-1);
Response.Cookies.Add(cookie);
}
Although the back function on the browser took me back and displayed the secured menu (I am still working on that) I was not able to do anything that was secured in the app.
Hope this helps
I've tried most answers in this thread, no luck. Ended up with this:
protected void btnLogout_Click(object sender, EventArgs e)
{
FormsAuthentication.Initialize();
var fat = new FormsAuthenticationTicket(1, "", DateTime.Now, DateTime.Now.AddMinutes(-30), false, string.Empty, FormsAuthentication.FormsCookiePath);
Response.Cookies.Add(new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(fat)));
FormsAuthentication.RedirectToLoginPage();
}
Found it here: http://forums.asp.net/t/1306526.aspx/1
This started happening to me when I set the authentication > forms > Path property in Web.config. Removing that fixed the problem, and a simple FormsAuthentication.SignOut(); again removed the cookie.
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).
I just had the same problem, where SignOut() seemingly failed to properly remove the ticket. But only in a specific case, where some other logic caused a redirect. After I removed this second redirect (replaced it with an error message), the problem went away.
The problem must have been that the page redirected at the wrong time, hence not triggering authentication.
I am having a similar issue now and I believe the problem in my case as well as the original poster is because of the redirect. By default a Response.Redirect causes an exception which immediately bubbles up until it is caught and the redirect is immediately executed, I am guessing that this is preventing the modified cookie collection from being passed down to the client. If you modify your code to use:
Response.Redirect("url", false);
This prevents the exception and seems to allow the cookie to be properly sent back to the client.
Just try to send a session variable when you press log in.
And on the welcome page, first check whether that session is empty like this in the page load or in the Init Event:
if(Session["UserID"] == null || Session["UserID"] == "")
{
Response.Redirect("Login.aspx");
}
I wanted to add some information to help understand the problem. Forms Authentication allows for storing user data either in a cookie, or in the query string of the URL. The method your site supports can be configured in the web.config file.
According to Microsoft:
The SignOut method removes the forms-authentication ticket information
from the cookie or the URL if CookiesSupported is false.
At the same time, they say:
One of the HttpCookieMode values that indicates whether the
application is configured for cookieless forms authentication. The
default is UseDeviceProfile.
Lastly, regarding UseDeviceProfile, they say:
If the CookieMode property is set to UseDeviceProfile, the
CookiesSupported property will return true if the Browser for the
current Request supports both cookies and redirecting with cookies;
otherwise, the CookiesSupported property will return false.
Piecing this all together, depending on the user's browser, the default configuration may result in CookiesSupported being true, which means the SignOut method doesn't clear the ticket from the cookie. This seems counter-intuitive and I don't know why it works this way -- I would expect SignOut to actually sign the user out under any circumstances.
One way to make the SignOut work by itself is to change the cookie mode to "UseCookies" (i.e. cookies are required) in the web.config file:
<authentication mode="Forms">
<forms loginUrl="~/Account/SignIn" cookieless="UseCookies"/>
</authentication>
According to my tests, doing this makes SignOut work by itself at the cost of your site now requiring cookies to function properly.
For me, the following approach works. I think if there is any error after the "FormsAuthentication.SignOut()" statement, SingOut doesn't work.
public ActionResult SignOut()
{
if (Request.IsAuthenticated)
{
FormsAuthentication.SignOut();
return Redirect("~/");
}
return View();
}
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.)
Doing Session.abandon() and destroying the cookie works pretty good. I'm using mvc3 and it looks like the problem occurs if you go to a protected page, log out, and go via your browser history. Not a big deal but still kinda of annoying.
Trying to go through links on my web app works the right way though.
Setting it to not do browser caching may be the way to go.
For MVC this works for me:
public ActionResult LogOff()
{
FormsAuthentication.SignOut();
return Redirect(FormsAuthentication.GetRedirectUrl(User.Identity.Name, true));
}
Be aware that WIF refuses to tell the browser to cleanup the cookies if the wsignoutcleanup message from STS doesn't match the url with the name of the application from IIS, and I mean CASE SENSITIVE. WIF responds with the green OK check, but will not send the command to delete cookies to browser.
So, you need to pay attention to the case sensitivity of your url's.
For example, ThinkTecture Identity Server saves the urls of the visiting RPs in one cookie, but it makes all of them lower case. WIF will receive the wsignoutcleanup message in lower case and will compare it with the application name in IIS. If it doesn't match, it deletes no cookies, but will report OK to the browser. So, for this Identity Server I needed to write all urls in web.config and all application names in IIS in lower case, in order to avoid such problems.
Also don't forget to allow third party cookies in the browser if you have the applications outside of the subdomain of STS, otherwise the browser will not delete the cookies even if WIF tells him so.
I am having trouble with the .Expires cookie attribute. It keeps coming back with 01/01/0001 12:00 AM, when I read the cookie back.
Here is the code. I added in the retrieve just below the save solely for debugging purposes. The save and retrieve happen in different places in the same file. I purposely did not specify a Domain, as I want the cookie to exist site wide.
The data shows up nicely, just not the expiration.
Note: I am testing under Visual Studio 2012 running under local host using .Net Framework 4.
System.Web.UI.Page oPage = this.Page;
HttpCookie oCookie = new HttpCookie("UserData");
// Set the cookie value.
oCookie.Secure = false;
oCookie["Field1"] = strField1;
oCookie["Field2"] = strField2;
oCookie.Expires = DateTime.Now.AddDays(1);
// Add the cookie.
oPage.Response.Cookies.Add(oCookie);
// Get the cookie.
oCookie = new HttpCookie("UserData");
oCookie = oPage.Request.Cookies["UserData"];
The browser will not send anything to the server except the cookie name and value. All of the other properties (expires, domain, path, httponly, ...) cannot be retrieved on requests after the cookie has been set.
The more accepted way to deal with this is to redirect the user to a login page when they try to access a protected resource and display some message along the lines of "You need to log in to view this page. If you were previously logged in, your session may have expired."
(Also note that you should be re-setting the cookie on every request, so that the user will not be logged out if they continue to use the site. It's not clear from your code whether you are doing this or not.)
I was just doing some more Google searching on my problem and saw this link, another posting here on Stackoverflow.
Cookies are always expired
I am also validating using the construct:
if (cookie != null && cookie.Expires > DateTime.Now)...
As several pointed out, expiration checking happens, if you can no longer retrieve the cookie. That is seriously dumb on whomever constructed this architecture. Yes, maybe there should be RequestCookie and ResponseCookie, the difference being ResponseCookie has no Expiry date.
The person who resopnded to me taught me that it is not just expires but other fields too.
In C# code, if using Form Authentication, You can find if cookie is persistent using below code
bool IsCookiePersistent = ((FormsIdentity)User.Identity).Ticket.IsPersistent;
Here Ticket will return the FormsAuthenticationTicket which has Expiration DateTime property.
Why does the property SessionID on the Session-object in an ASP.NET-page change between requests?
I have a page like this:
...
<div>
SessionID: <%= SessionID %>
</div>
...
And the output keeps changing every time I hit F5, independent of browser.
This is the reason
When using cookie-based session state, ASP.NET does not allocate storage for session data until the Session object is used. As a result, a new session ID is generated for each page request until the session object is accessed. If your application requires a static session ID for the entire session, you can either implement the Session_Start method in the application's Global.asax file and store data in the Session object to fix the session ID, or you can use code in another part of your application to explicitly store data in the Session object.
http://msdn.microsoft.com/en-us/library/system.web.sessionstate.httpsessionstate.sessionid.aspx
So basically, unless you access your session object on the backend, a new sessionId will be generated with each request
EDIT
This code must be added on the file Global.asax. It adds an entry to the Session object so you fix the session until it expires.
protected void Session_Start(Object sender, EventArgs e)
{
Session["init"] = 0;
}
There is another, more insidious reason, why this may occur even when the Session object has been initialized as demonstrated by Cladudio.
In the Web.config, if there is an <httpCookies> entry that is set to requireSSL="true" but you are not actually using HTTPS: for a specific request, then the session cookie is not sent (or maybe not returned, I'm not sure which) which means that you end up with a brand new session for each request.
I found this one the hard way, spending several hours going back and forth between several commits in my source control, until I found what specific change had broken my application.
In my case I figured out that the session cookie had a domain that included www. prefix, while I was requesting page with no www..
Adding www. to the URL immediately fixed the problem. Later I changed cookie's domain to be set to .mysite.com instead of www.mysite.com.
my problem was that we had this set in web.config
<httpCookies httpOnlyCookies="true" requireSSL="true" />
this means that when debugging in non-SSL (the default), the auth cookie would not get sent back to the server. this would mean that the server would send a new auth cookie (with a new session) for every request back to the client.
the fix is to either set requiressl to false in web.config and true in web.release.config or turn on SSL while debugging:
Using Neville's answer (deleting requireSSL = true, in web.config) and slightly modifying Joel Etherton's code, here is the code that should handle a site that runs in both SSL mode and non SSL mode, depending on the user and the page (I am jumping back into code and haven't tested it on SSL yet, but expect it should work - will be too busy later to get back to this, so here it is:
if (HttpContext.Current.Response.Cookies.Count > 0)
{
foreach (string s in HttpContext.Current.Response.Cookies.AllKeys)
{
if (s == FormsAuthentication.FormsCookieName || s.ToLower() == "asp.net_sessionid")
{
HttpContext.Current.Response.Cookies[s].Secure = HttpContext.Current.Request.IsSecureConnection;
}
}
}
Another possibility that causes the SessionID to change between requests, even when Session_OnStart is defined and/or a Session has been initialized, is that the URL hostname contains an invalid character (such as an underscore). I believe this is IE specific (not verified), but if your URL is, say, http://server_name/app, then IE will block all cookies and your session information will not be accessible between requests.
In fact, each request will spin up a separate session on the server, so if your page contains multiple images, script tags, etc., then each of those GET requests will result in a different session on the server.
Further information: http://support.microsoft.com/kb/316112
My issue was with a Microsoft MediaRoom IPTV application. It turns out that MPF MRML applications don't support cookies; changing to use cookieless sessions in the web.config solved my issue
<sessionState cookieless="true" />
Here's a REALLY old article about it:
Cookieless ASP.NET
in my case it was because I was modifying session after redirecting from a gateway in an external application, so because I was using IP instead on localhost in that page url it was actually considered different website with different sessions.
In summary
pay more attention if you are debugging a hosted application on IIS instead of IIS express and mixing your machine http://Ip and http://localhost in various pages
In my case this was happening a lot in my development and test environments. After trying all of the above solutions without any success I found that I was able to fix this problem by deleting all session cookies. The web developer extension makes this very easy to do. I mostly use Firefox for testing and development, but this also happened while testing in Chrome. The fix also worked in Chrome.
I haven't had to do this yet in the production environment and have not received any reports of people not being able to log in. This also only seemed to happen after making the session cookies to be secure. It never happened in the past when they were not secure.
Update: this only started happening after we changed the session cookie to make it secure. I've determined that the exact issue was caused by there being two or more session cookies in the browser with the same path and domain. The one that was always the problem was the one that had an empty or null value. After deleting that particular cookie the issue was resolved. I've also added code in Global.asax.cs Sessin_Start method to check for this empty cookie and if so set it's expiration date to something in the past.
HttpCookieCollection cookies = Response.Cookies;
for (int i = 0; i < cookies.Count; i++)
{
HttpCookie cookie = cookies.Get(i);
if (cookie != null)
{
if ((cookie.Name == "ASP.NET_SessionId" || cookie.Name == "ASP.NET_SessionID") && String.IsNullOrEmpty(cookie.Value))
{
//Try resetting the expiration date of the session cookie to something in the past and/or deleting it.
//Reset the expiration time of the cookie to one hour, one minute and one second in the past
if (Response.Cookies[cookie.Name] != null)
Response.Cookies[cookie.Name].Expires = DateTime.Today.Subtract(new TimeSpan(1, 1, 1));
}
}
}
This was changing for me beginning with .NET 4.7.2 and it was due to the SameSite property on the session cookie. See here for more info: https://devblogs.microsoft.com/aspnet/upcoming-samesite-cookie-changes-in-asp-net-and-asp-net-core/
The default value changed to "Lax" and started breaking things. I changed it to "None" and things worked as expected.
Be sure that you do not have a session timeout that is very short, and also make sure that if you are using cookie based sessions that you are accepting the session.
The FireFox webDeveloperToolbar is helpful at times like this as you can see the cookies set for your application.
Session ID resetting may have many causes. However any mentioned above doesn't relate to my problem. So I'll describe it for future reference.
In my case a new session created on each request resulted in infinite redirect loop. The redirect action takes place in OnActionExecuting event.
Also I've been clearing all http headers (also in OnActionExecuting event using Response.ClearHeaders method) in order to prevent caching sites on client side. But that method clears all headers including informations about user's session, and consequently all data in Temp storage (which I was using later in program). So even setting new session in Session_Start event didn't help.
To resolve my problem I ensured not to remove the headers when a redirection occurs.
Hope it helps someone.
I ran into this issue a different way. The controllers that had this attribute [SessionState(SessionStateBehavior.ReadOnly)] were reading from a different session even though I had set a value in the original session upon app startup. I was adding the session value via the _layout.cshtml (maybe not the best idea?)
It was clearly the ReadOnly causing the issue because when I removed the attribute, the original session (and SessionId) would stay in tact. Using Claudio's/Microsoft's solution fixed it.
I'm on .NET Core 2.1 and I'm well aware that the question isn't about Core. Yet the internet is lacking and Google brought me here so hoping to save someone a few hours.
Startup.cs
services.AddCors(o => o.AddPolicy("AllowAll", builder =>
{
builder
.WithOrigins("http://localhost:3000") // important
.AllowCredentials() // important
.AllowAnyMethod()
.AllowAnyHeader(); // obviously just for testing
}));
client.js
const resp = await fetch("https://localhost:5001/api/user", {
method: 'POST',
credentials: 'include', // important
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify(data)
})
Controllers/LoginController.cs
namespace WebServer.Controllers
{
[Route("api/[controller]")]
[ApiController]
public class UserController : ControllerBase
{
[HttpPost]
public IEnumerable<string> Post([FromBody]LoginForm lf)
{
string prevUsername = HttpContext.Session.GetString("username");
Console.WriteLine("Previous username: " + prevUsername);
HttpContext.Session.SetString("username", lf.username);
return new string[] { lf.username, lf.password };
}
}
}
Notice that the session writing and reading works, yet no cookies seem to be passed to the browser. At least I couldn't find a "Set-Cookie" header anywhere.
After checking a user's credentials and confirming they are good, I'm using FormsAuthentication.SetAuthCookie("Username", false); to authenticate the user.
In the masterpage I then use Page.User.Identity.IsAuthenticated to make sure we're dealing with a logged in user and not a guest.
The problem lies in first setting the auth cookie. When I set the auth cookie, immediately afterwards I run a method that uses Page.User.Identity.IsAuthenticated to change the welcome message from a generic "Welcome, guest!" message to a more personal "Welcome, username!" message. This does not work until I go to another page, so I know the login process has worked, but it seems I cannot access the information I need until a refresh or a redirect happens.
Do I need to redirect the user after setting the auth cookie in order use Page.User.Identity.IsAuthenticated to change the message?
I have seen this before so I know the answer is yes. (As in, yes you do need to redirect the user to correctly use Page.User.Identity.IsAuthenticated)
What I imagine is the cause is because IsAuthenticated evaluates the current request, and when the current request first came in it was recorded as not authenticated.
What you will need to do is apply whatever logic you have in said method without the check for IsAuthenicated (make it assume true).
Now I don't know the details of your method as to suggest how to re-factor it to cope with this, but you could split out the "Do Stuff" part into a separate function which you could then call directly from you login function to bypass the authentication check.
EDIT: To back up my assumption you can read this page.
The interesting part:
The forms-authentication ticket supplies forms-authentication
information to the next request made by the browser.
I'd like to point out that there's actually a way around this (since I've never seen this said in any other question like this). You can retrieve the cookie and its data where User.Identity's information comes from without a redirect. The thing is, the cookie just hasn't been sent to the browser yet.
It simply gets the cookie made by FormsAuthentication from the Response.Cookies object:
HttpCookie EncryptedCookie = Response.Cookies.Get(FormsAuthentication.FormsCookieName);
FormsAuthenticationTicket DecryptedCookie;
try {
DecryptedCookie = FormsAuthentication.Decrypt(EncryptedCookie.Value);
} catch (ArgumentException) {
// Not a valid cookie
return false;
}
// DecryptedCookie.Name: The Username
// DecryptedCookie.UserData: Any additional data, as a string. This isn't normally used
return !DecryptedCookie.Expired;
I have a page where I need to check for the presence of a cookie and then perform a redirect.
I have the code written (ASP.NET) to detect the cookie and perform a redirect. Pseudo-code:
HttpCookie myCookie = Request.Cookies.Get("theCookie");
if(myCookie == null)
{
myCookie = new HttpCookie("theCookie","myValue")
response.Redirect("page.aspx"); //Redirect to check for the presence of the cookie
}
More code...
When the user has cookies enabled, this approach works fine. When they have cookies disabled, however, they wind up stuck in an infinite loop (the page attempts to create the cookie, redirects, sees no cookie, then redirects again, ad infinitum). Most human users are probably going to be OK, but this will probably do a number on the site's SEO ratings.
I've wracked my brain for solutions, and since cookies are out of the question, that leaves viewstate and querystrings.
Because I've got to do a redirect, I think I'm stuck with querystrings. The problem is in order to detect whether a page has already been hit, I need to append a querystring to prevent the redirect from kicking in again.
Can anyone think of a way to accomplish this (preventing a redirect) without using cookies, viewstate, or querystrings? I think the answer is probably no...
Using a querystring in the manner you have described is the correct solution.
EDIT: looks like bad idea - query string is the approach. Keeping for reference: local storage as well as script can be disabled, so it needs to be considered when designing any client side detection logic.
You can also try to use local storage in browser to prevent infinite redirects. It will allow you to keep url clean from "?isCookie=true" query string. Note that you need JavaScript enabled for that. If you worried about cookies you should be worried about JavaScript disabled too.
What I wound up doing (in case someone else tries this) was using a couple of tricks:
Set up an ASP.NET hidden field control with its value set to false (default - cookies are disabled)
Used client-side script to check whether cookies are enabled
If the cookie gets set, cookies are enabled. In this case I use a jQuery call to change the value of the hidden field from false to true
Server-side, if the value of the hidden field is true, the page does the redirect. Otherwise, it just continues processing the page.
If the user has Javascript disabled, the value of the hidden field remains false, so the page is still rendered only once.
Thanks for letting me talk through it and getting me thinking!