How can I suppress the browser's authentication dialog?

Question

My web application has a login page that submits authentication credentials via an AJAX call. If the user enters the correct username and password, everything is fine, but if not, the following happens:

1. The web server determines that although the request included a well-formed Authorization header, the credentials in the header do not successfully authenticate.
2. The web server returns a 401 status code and includes one or more WWW-Authenticate headers listing the supported authentication types.
3. The browser detects that the response to my call on the XMLHttpRequest object is a 401 and the response includes WWW-Authenticate headers. It then pops up an authentication dialog asking, again, for the username and password.

This is all fine up until step 3. I don't want the dialog to pop up, I want want to handle the 401 response in my AJAX callback function. (For example, by displaying an error message on the login page.) I want the user to re-enter their username and password, of course, but I want them to see my friendly, reassuring login form, not the browser's ugly, default authentication dialog.

Incidentally, I have no control over the server, so having it return a custom status code (i.e., something other than a 401) is not an option.

Is there any way I can suppress the authentication dialog? In particular, can I suppress the Authentication Required dialog in Firefox 2 or later? Is there any way to suppress the Connect to [host] dialog in IE 6 and later?

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Edit
Additional information from the author (Sept. 18):
I should add that the real problem with the browser's authentication dialog popping up is that it give insufficient information to the user.

The user has just entered a username and password via the form on the login page, he believes he has typed them both correctly, and he has clicked the submit button or hit enter. His expectation is that he will be taken to the next page or perhaps told that he has entered his information incorrectly and should try again. However, he is instead presented with an unexpected dialog box.

The dialog makes no acknowledgment of the fact he just did enter a username and password. It does not clearly state that there was a problem and that he should try again. Instead, the dialog box presents the user with cryptic information like "The site says: '[realm]'." Where [realm] is a short realm name that only a programmer could love.

Web broswer designers take note: no one would ask how to suppress the authentication dialog if the dialog itself were simply more user-friendly. The entire reason that I am doing a login form is that our product management team rightly considers the browsers' authentication dialogs to be awful.

Answer 1

I don't think this is possible -- if you use the browser's HTTP client implementation, it will always pop up that dialog. Two hacks come to mind:

1. Maybe Flash handles this differently (I haven't tried yet), so having a flash movie make the request might help.

2. You can set up a 'proxie' for the service that you're accessing on your own server, and have it modify the authentication headers a bit, so that the browser doesn't recognise them.

Answer 2

I encountered the same issue here, and the backend engineer at my company implemented a behavior that is apparently considered a good practice : when a call to a URL returns a 401, if the client has set the header X-Requested-With: XMLHttpRequest, the server drops the www-authenticate header in its response.

The side effect is that the default authentication popup does not appear.

Make sure that your API call has the X-Requested-With header set to XMLHttpRequest. If so there is nothing to do except changing the server behavior according to this good practice...

Answer 3

The browser pops up a login prompt when both of the following conditions are met:

1. HTTP status is 4xx
2. WWW-Authenticate header is present in the response

If you can control the HTTP response, then you can remove the WWW-Authenticate header from the response, and the browser won't popup the login dialog.

If you can't control the response, you can setup a proxy to filter out the WWW-Authenticate header from the response.

As far as I know (feel free to correct me if I'm wrong), there is no way to prevent the login prompt once the browser receives the WWW-Authenticate header.

Answer 4

I realize that this question and its answers are very old. But, I ended up here. Perhaps others will as well.

If you have access to the code for the web service that is returning the 401. Simply change the service to return a 403 (Forbidden) in this situation instead 401. The browser will not prompt for credentials in response to a 403. 403 is the correct code for an authenticated user that is not authorized for a specific resource. Which seems to be the situation of the OP.

From the IETF document on 403:

A server that receives valid credentials that are not adequate to gain access ought to respond with the 403 (Forbidden) status code

Answer 5

In Mozilla you can achieve it with the following script when you create the XMLHttpRequest object:

xmlHttp=new XMLHttpRequest();
xmlHttp.mozBackgroundRequest = true;
xmlHttp.open("GET",URL,true,USERNAME,PASSWORD);
xmlHttp.send(null);

The 2nd line prevents the dialog box....

Answer 6

What server technology do you use and is there a particular product you use for authentication?

Since the browser is only doing its job, I believe you have to change things on the server side to not return a 401 status code. This could be done using custom authentication forms that simply return the form again when the authentication fails.

Answer 7

In Mozilla land, setting the mozBackgroundRequest parameter of XMLHttpRequest (docs) to true suppresses those dialogs and causes the requests to simply fail. However, I don't know how good cross-browser support is (including whether the the quality of the error info on those failed requests is very good across browsers.)

Answer 8

jan.vdbergh has the truth, if you can change the 401 on server side for another status code, the browser won't catch and paint the pop-up. Another solution could be change the WWW-Authenticate header for another custom header. I dont't believe why the different browser can't support it, in a few versions of Firefox we can do the xhr request with mozBackgroundRequest, but in the other browsers?? here, there is an interesting link with this issue in Chromium.

Answer 9

I have this same issue with MVC 5 and VPN where whenever we are outside the DMZ using the VPN, we find ourselves having to answer this browser message. Using .net I simply handle the routing of the error using

<customErrors defaultRedirect="~/Error"  >
  <error statusCode="401" redirect="~/Index"/>
</customErrors>

thus far it has worked because the Index action under the home controller validates the user. The view in this action, if logon is unsuccessful, has login controls that I use to log the user in using using LDAP query passed into Directory Services:

      DirectoryEntry entry = new DirectoryEntry("LDAP://OurDomain");
      DirectorySearcher Dsearch = new DirectorySearcher(entry);
      Dsearch.Filter = "(SAMAccountName=" + UserID + ")";
      Dsearch.PropertiesToLoad.Add("cn");

While this has worked fine thus far, and I must let you know that I am still testing it and the above code has had no reason to run so it's subject to removal... testing currently includes trying to discover a case where the second set of code is of any more use. Again, this is a work in progress, but since it could be of some assistance or jog your brain for some ideas, I decided to add it now... I will update it with the final results once all testing is done.

Answer 10

For those unsing C# here's ActionAttribute that returns 400 instead of 401, and 'swallows' Basic auth dialog.

public class NoBasicAuthDialogAuthorizeAttribute : AuthorizeAttribute
{
    protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
    {
        base.HandleUnauthorizedRequest(filterContext);
        filterContext.Result = new HttpStatusCodeResult(400);
    }
}

use like following:

[NoBasicAuthDialogAuthorize(Roles = "A-Team")]
public ActionResult CarType()
{
 // your code goes here
}

Hope this saves you some time.

Answer 11

I'm using Node, Express & Passport and was struggling with the same issue. I got it to work by explicitly setting the www-authenticate header to an empty string. In my case, it looked like this:

(err, req, res, next) => {
  if (err) {
    res._headers['www-authenticate'] = ''
    return res.json(err)
  }
}

I hope that helps someone!