How to log out user from web site using BASIC authentication?

Question

Is it possible to log out user from a web site if he is using basic authentication?

Killing session is not enough, since, once user is authenticated, each request contains login info, so user is automatically logged in next time he/she access the site using the same credentials.

The only solution so far is to close browser, but that's not acceptable from the usability standpoint.

Answer 1

Basic Authentication wasn't designed to manage logging out. You can do it, but not completely automatically.

What you have to do is have the user click a logout link, and send a ‘401 Unauthorized’ in response, using the same realm and at the same URL folder level as the normal 401 you send requesting a login.

They must be directed to input wrong credentials next, eg. a blank username-and-password, and in response you send back a “You have successfully logged out” page. The wrong/blank credentials will then overwrite the previous correct credentials.

In short, the logout script inverts the logic of the login script, only returning the success page if the user isn't passing the right credentials.

The question is whether the somewhat curious “don't enter your password” password box will meet user acceptance. Password managers that try to auto-fill the password can also get in the way here.

Edit to add in response to comment: re-log-in is a slightly different problem (unless you require a two-step logout/login obviously). You have to reject (401) the first attempt to access the relogin link, than accept the second (which presumably has a different username/password). There are a few ways you could do this. One would be to include the current username in the logout link (eg. /relogin?username), and reject when the credentials match the username.

Answer 2

An addition to the answer by bobince ...

With Ajax you can have your 'Logout' link/button wired to a Javascript function. Have this function send the XMLHttpRequest with a bad username and password. This should get back a 401. Then set document.location back to the pre-login page. This way, the user will never see the extra login dialog during logout, nor have to remember to put in bad credentials.

Answer 3

Have the user click on a link to https://log:out@example.com/. That will overwrite existing credentials with invalid ones; logging them out.

Answer 4

You can do it entirely in JavaScript:

IE has (for a long time) standard API for clearing Basic Authentication cache:

document.execCommand("ClearAuthenticationCache")

Should return true when it works. Returns either false, undefined or blows up on other browsers.

New browsers (as of Dec 2012: Chrome, FireFox, Safari) have "magic" behavior. If they see a successful basic auth request with any bogus other username (let's say logout) they clear the credentials cache and possibly set it for that new bogus user name, which you need to make sure is not a valid user name for viewing content.

Basic example of that is:

var p = window.location.protocol + '//'
// current location must return 200 OK for this GET
window.location = window.location.href.replace(p, p + 'logout:password@')

An "asynchronous" way of doing the above is to do an AJAX call utilizing the logout username. Example:

(function(safeLocation){
    var outcome, u, m = "You should be logged out now.";
    // IE has a simple solution for it - API:
    try { outcome = document.execCommand("ClearAuthenticationCache") }catch(e){}
    // Other browsers need a larger solution - AJAX call with special user name - 'logout'.
    if (!outcome) {
        // Let's create an xmlhttp object
        outcome = (function(x){
            if (x) {
                // the reason we use "random" value for password is 
                // that browsers cache requests. changing
                // password effectively behaves like cache-busing.
                x.open("HEAD", safeLocation || location.href, true, "logout", (new Date()).getTime().toString())
                x.send("")
                // x.abort()
                return 1 // this is **speculative** "We are done." 
            } else {
                return
            }
        })(window.XMLHttpRequest ? new window.XMLHttpRequest() : ( window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : u ))
    }
    if (!outcome) {
        m = "Your browser is too old or too weird to support log out functionality. Close all windows and restart the browser."
    }
    alert(m)
    // return !!outcome
})(/*if present URI does not return 200 OK for GET, set some other 200 OK location here*/)

You can make it a bookmarklet too:

javascript:(function(c){var a,b="You should be logged out now.";try{a=document.execCommand("ClearAuthenticationCache")}catch(d){}a||((a=window.XMLHttpRequest?new window.XMLHttpRequest:window.ActiveXObject?new ActiveXObject("Microsoft.XMLHTTP"):void 0)?(a.open("HEAD",c||location.href,!0,"logout",(new Date).getTime().toString()),a.send(""),a=1):a=void 0);a||(b="Your browser is too old or too weird to support log out functionality. Close all windows and restart the browser.");alert(b)})(/*pass safeLocation here if you need*/);

Answer 5

The following function is confirmed working for Firefox 40, Chrome 44, Opera 31 and IE 11.
Bowser is used for browser detection, jQuery is also used.

- secUrl is the url to a password protected area from which to log out.
- redirUrl is the url to a non password protected area (logout success page).
- you might wish to increase the redirect timer (currently 200ms).

function logout(secUrl, redirUrl) {
    if (bowser.msie) {
        document.execCommand('ClearAuthenticationCache', 'false');
    } else if (bowser.gecko) {
        $.ajax({
            async: false,
            url: secUrl,
            type: 'GET',
            username: 'logout'
        });
    } else if (bowser.webkit) {
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.open("GET", secUrl, true);
        xmlhttp.setRequestHeader("Authorization", "Basic logout");
        xmlhttp.send();
    } else {
        alert("Logging out automatically is unsupported for " + bowser.name
            + "\nYou must close the browser to log out.");
    }
    setTimeout(function () {
        window.location.href = redirUrl;
    }, 200);
}

Answer 6

This isn't directly possible with Basic-Authentication.

There's no mechanism in the HTTP specification for the server to tell the browser to stop sending the credentials that the user already presented.

There are "hacks" (see other answers) typically involving using XMLHttpRequest to send an HTTP request with incorrect credentials to overwrite the ones originally supplied.

Answer 7

Here's a very simple Javascript example using jQuery:

function logout(to_url) {
    var out = window.location.href.replace(/:\/\//, '://log:out@');

    jQuery.get(out).error(function() {
        window.location = to_url;
    });
}

This log user out without showing him the browser log-in box again, then redirect him to a logged out page

Answer 8

It's actually pretty simple.

Just visit the following in your browser and use wrong credentials: http://username:password@yourdomain.com

That should "log you out".

Answer 9

This is working for IE/Netscape/Chrome :

      function ClearAuthentication(LogOffPage) 
  {
     var IsInternetExplorer = false;    

     try
     {
         var agt=navigator.userAgent.toLowerCase();
         if (agt.indexOf("msie") != -1) { IsInternetExplorer = true; }
     }
     catch(e)
     {
         IsInternetExplorer = false;    
     };

     if (IsInternetExplorer) 
     {
        // Logoff Internet Explorer
        document.execCommand("ClearAuthenticationCache");
        window.location = LogOffPage;
     }
     else 
     {
        // Logoff every other browsers
    $.ajax({
         username: 'unknown',
         password: 'WrongPassword',
             url: './cgi-bin/PrimoCgi',
         type: 'GET',
         beforeSend: function(xhr)
                 {
            xhr.setRequestHeader("Authorization", "Basic AAAAAAAAAAAAAAAAAAA=");
         },

                 error: function(err)
                 {
                    window.location = LogOffPage;
             }
    });
     }
  }


  $(document).ready(function () 
  {
      $('#Btn1').click(function () 
      {
         // Call Clear Authentication 
         ClearAuthentication("force_logout.html"); 
      });
  });          

Answer 10

function logout() {
  var userAgent = navigator.userAgent.toLowerCase();

  if (userAgent.indexOf("msie") != -1) {
    document.execCommand("ClearAuthenticationCache", false);
  }

  xhr_objectCarte = null;

  if(window.XMLHttpRequest)
    xhr_object = new XMLHttpRequest();
  else if(window.ActiveXObject)
    xhr_object = new ActiveXObject("Microsoft.XMLHTTP");
  else
    alert ("Your browser doesn't support XMLHTTPREQUEST");

  xhr_object.open ('GET', 'http://yourserver.com/rep/index.php', false, 'username', 'password');
  xhr_object.send ("");
  xhr_object = null;

  document.location = 'http://yourserver.com'; 
  return false;
}

Answer 11

 function logout(url){
    var str = url.replace("http://", "http://" + new Date().getTime() + "@");
    var xmlhttp;
    if (window.XMLHttpRequest) xmlhttp=new XMLHttpRequest();
    else xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    xmlhttp.onreadystatechange=function()
    {
        if (xmlhttp.readyState==4) location.reload();
    }
    xmlhttp.open("GET",str,true);
    xmlhttp.setRequestHeader("Authorization","Basic xxxxxxxxxx")
    xmlhttp.send();
    return false;
}

Answer 12

All you need is redirect user on some logout URL and return 401 Unauthorized error on it. On error page (which must be accessible without basic auth) you need to provide a full link to your home page (including scheme and hostname). User will click this link and browser will ask for credentials again.

Example for Nginx:

location /logout {
    return 401;
}

error_page 401 /errors/401.html;

location /errors {
    auth_basic off;
    ssi        on;
    ssi_types  text/html;
    alias /home/user/errors;
}

Error page /home/user/errors/401.html:

<!DOCTYPE html>
<p>You're not authorised. <a href="<!--# echo var="scheme" -->://<!--# echo var="host" -->/">Login</a>.</p>

Answer 13

This JavaScript must be working for all latest version browsers:

//Detect Browser
var isOpera = !!window.opera || navigator.userAgent.indexOf(' OPR/') >= 0;
    // Opera 8.0+ (UA detection to detect Blink/v8-powered Opera)
var isFirefox = typeof InstallTrigger !== 'undefined';   // Firefox 1.0+
var isSafari = Object.prototype.toString.call(window.HTMLElement).indexOf('Constructor') > 0;
    // At least Safari 3+: "[object HTMLElementConstructor]"
var isChrome = !!window.chrome && !isOpera;              // Chrome 1+
var isIE = /*@cc_on!@*/false || !!document.documentMode; // At least IE6
var Host = window.location.host;


//Clear Basic Realm Authentication
if(isIE){
//IE
    document.execCommand("ClearAuthenticationCache");
    window.location = '/';
}
else if(isSafari)
{//Safari. but this works mostly on all browser except chrome
    (function(safeLocation){
        var outcome, u, m = "You should be logged out now.";
        // IE has a simple solution for it - API:
        try { outcome = document.execCommand("ClearAuthenticationCache") }catch(e){}
        // Other browsers need a larger solution - AJAX call with special user name - 'logout'.
        if (!outcome) {
            // Let's create an xmlhttp object
            outcome = (function(x){
                if (x) {
                    // the reason we use "random" value for password is 
                    // that browsers cache requests. changing
                    // password effectively behaves like cache-busing.
                    x.open("HEAD", safeLocation || location.href, true, "logout", (new Date()).getTime().toString())
                    x.send("");
                    // x.abort()
                    return 1 // this is **speculative** "We are done." 
                } else {
                    return
                }
            })(window.XMLHttpRequest ? new window.XMLHttpRequest() : ( window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : u )) 
        }
        if (!outcome) {
            m = "Your browser is too old or too weird to support log out functionality. Close all windows and restart the browser."
        }
        alert(m);
        window.location = '/';
        // return !!outcome
    })(/*if present URI does not return 200 OK for GET, set some other 200 OK location here*/)
}
else{
//Firefox,Chrome
    window.location = 'http://log:out@'+Host+'/';
}

Answer 14

add this to your application :

@app.route('/logout')
def logout():
    return ('Logout', 401, {'WWW-Authenticate': 'Basic realm="Login required"'})

Answer 15

Based on what I read above I got a simple solution that works on any browser:

1) on you logout page you call an ajax to your login back end. Your login back end must accept logout user. Once the back end accept, the browser clear the current user and assumes the "logout" user.

$.ajax({
    async: false,
    url: 'http://your_login_backend',
    type: 'GET',
    username: 'logout'
});      

setTimeout(function () {
    window.location.href = 'http://normal_index';
}, 200);

2) Now when the user got back to the normal index file it will try to automatic enter in the system with the user "logout", on this second time you must block it by reply with 401 to invoke the login/password dialog.

3) There are many ways to do that, I created two login back ends, one that accepts the logout user and one that doesn't. My normal login page use the one that doesn't accept, my logout page use the one that accepts it.

Answer 16

• use a session ID (cookie)
• invalidate the session ID on the server
• Don't accept users with invalid session IDs

Answer 17

I updated mthoring's solution for modern Chrome versions:

function logout(secUrl, redirUrl) {
    if (bowser.msie) {
        document.execCommand('ClearAuthenticationCache', 'false');
    } else if (bowser.gecko) {
        $.ajax({
            async: false,
            url: secUrl,
            type: 'GET',
            username: 'logout'
        });
    } else if (bowser.webkit || bowser.chrome) {
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.open(\"GET\", secUrl, true);
        xmlhttp.setRequestHeader(\"Authorization\", \"Basic logout\");\
        xmlhttp.send();
    } else {
// http://stackoverflow.com/questions/5957822/how-to-clear-basic-authentication-details-in-chrome
        redirUrl = url.replace('http://', 'http://' + new Date().getTime() + '@');
    }
    setTimeout(function () {
        window.location.href = redirUrl;
    }, 200);
}

Answer 18

    function logout(secUrl, redirUrl) {
        if (bowser.msie) {
            document.execCommand('ClearAuthenticationCache', 'false');
        } else if (bowser.gecko) {
            $.ajax({
                async: false,
                url: secUrl,
                type: 'GET',
                username: 'logout'
            });
        } else if (bowser.webkit) {
            var xmlhttp = new XMLHttpRequest();
            xmlhttp.open("GET", secUrl, true);
            xmlhttp.setRequestHeader("Authorization", "Basic logout");
            xmlhttp.send();
        } else {
            alert("Logging out automatically is unsupported for " + bowser.name
                + "\nYou must close the browser to log out.");
        }
        setTimeout(function () {
            window.location.href = redirUrl;
        }, 200);
    }

I tried using the above in the following way.

?php
    ob_start();
    session_start();
    require_once 'dbconnect.php';

    // if session is not set this will redirect to login page
    if( !isset($_SESSION['user']) ) {
        header("Location: index.php");
        exit;
    }
    // select loggedin users detail
    $res=mysql_query("SELECT * FROM users WHERE userId=".$_SESSION['user']);
    $userRow=mysql_fetch_array($res);
?>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Welcome - <?php echo $userRow['userEmail']; ?></title>
<link rel="stylesheet" href="assets/css/bootstrap.min.css" type="text/css"  />
<link rel="stylesheet" href="style.css" type="text/css" />

    <script src="assets/js/bowser.min.js"></script>
<script>
//function logout(secUrl, redirUrl)
//bowser = require('bowser');
function logout(secUrl, redirUrl) {
alert(redirUrl);
    if (bowser.msie) {
        document.execCommand('ClearAuthenticationCache', 'false');
    } else if (bowser.gecko) {
        $.ajax({
            async: false,
            url: secUrl,
            type: 'GET',
            username: 'logout'
        });
    } else if (bowser.webkit) {
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.open("GET", secUrl, true);
        xmlhttp.setRequestHeader("Authorization", "Basic logout");
        xmlhttp.send();
    } else {
        alert("Logging out automatically is unsupported for " + bowser.name
            + "\nYou must close the browser to log out.");
    }
    window.location.assign(redirUrl);
    /*setTimeout(function () {
        window.location.href = redirUrl;
    }, 200);*/
}


function f1()
    {
       alert("f1 called");
       //form validation that recalls the page showing with supplied inputs.    
    }
</script>
</head>
<body>

    <nav class="navbar navbar-default navbar-fixed-top">
      <div class="container">
        <div class="navbar-header">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
            <span class="sr-only">Toggle navigation</span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
          </button>
          <a class="navbar-brand" href="http://www.codingcage.com">Coding Cage</a>
        </div>
        <div id="navbar" class="navbar-collapse collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="http://www.codingcage.com/2015/01/user-registration-and-login-script-using-php-mysql.html">Back to Article</a></li>
            <li><a href="http://www.codingcage.com/search/label/jQuery">jQuery</a></li>
            <li><a href="http://www.codingcage.com/search/label/PHP">PHP</a></li>
          </ul>
          <ul class="nav navbar-nav navbar-right">

            <li class="dropdown">
              <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">
              <span class="glyphicon glyphicon-user"></span>&nbsp;Hi' <?php echo $userRow['userEmail']; ?>&nbsp;<span class="caret"></span></a>
              <ul class="dropdown-menu">
                <li><a href="logout.php?logout"><span class="glyphicon glyphicon-log-out"></span>&nbsp;Sign Out</a></li>
              </ul>
            </li>
          </ul>
        </div><!--/.nav-collapse -->
      </div>
    </nav> 

    <div id="wrapper">

    <div class="container">

        <div class="page-header">
        <h3>Coding Cage - Programming Blog</h3>
        </div>

        <div class="row">
        <div class="col-lg-12" id="div_logout">
        <h1 onclick="logout(window.location.href, 'www.espncricinfo.com')">MichaelA1S1! Click here to see log out functionality upon click inside div</h1>
        </div>
        </div>

    </div>

    </div>

    <script src="assets/jquery-1.11.3-jquery.min.js"></script>
    <script src="assets/js/bootstrap.min.js"></script>


</body>
</html>
<?php ob_end_flush(); ?>

But it only redirects you to new location. No logout.

Answer 19

type chrome://restart in the address bar and chrome, with all its apps that are running in background, will restart and the Auth password cache will be cleaned.