Quick setup

Adding the Persona login system to your site takes just five steps:

  1. Include the Persona JavaScript library on your pages.
  2. Add “login” and “logout” buttons.
  3. Watch for login and logout actions.
  4. Verify the user’s credentials.
  5. Review best practices.

You should be able to get up and running in a single afternoon, but first things first: If you’re going to use Persona on your site, please take a moment and subscribe to the Persona notices mailing list. It’s extremely low traffic, only being used to announce changes or security issues which may adversely impact your site.

Step 1: Include the Persona library

Persona is designed to be browser-neutral and works well on all major desktop and mobile browsers.

In the future we expect browsers to provide native support for Persona, but in the meantime we provide a JavaScript library that fully implements the user interface and client-side part of the protocol. By including this library, your users will be able to sign in with Persona whether or not their browser has native support.

Once this library is loaded in your page, the Persona functions you need (watch(), request(), and logout()) will be available in the global navigator.id object.

To include the Persona JavaScript library, you can place this script tag at the bottom of the page body:

<script src="https://login.persona.org/include.js"></script>

You must include this on every page which uses navigator.id functions. Because Persona is still in development, you should not self-host the include.js file.

Suppressing Compatibility Mode

You should also make sure users of Internet Explorer can't use Compatibility Mode, as this will break Persona. To do this:

  • either include <meta http-equiv="X-UA-Compatible" content="IE=Edge"> on your page, before any script elements
  • or set the following HTTP header on your page: X-UA-Compatible: IE=Edge.

For more information, see the notes in IE Compatibility Mode and "IE8 and IE9 Complications".

Step 2: Add login and logout buttons

Because Persona is designed as a DOM API, you must call functions when a user clicks a login or logout button on your site. To open the Persona dialog and prompt the user to log in, you should invoke navigator.id.request(). For logout, invoke navigator.id.logout(). Note, the call to logout() must be made in the click handler of the logout button.

For example:

var signinLink = document.getElementById('signin');
if (signinLink) {
  signinLink.onclick = function() { navigator.id.request(); };
}

var signoutLink = document.getElementById('signout');
if (signoutLink) {
  signoutLink.onclick = function() { navigator.id.logout(); };
}

What should those buttons look like? Check out our Branding Resources page for premade images and CSS-based buttons!

Step 3: Watch for login and logout actions

For Persona to function, you need to tell it what to do when a user logs in or out. This is done by calling the navigator.id.watch() function and supplying three parameters:

  1. The email address of the user currently logged into your site from this computer, or null if no one is logged in. For example, you might examine the browser's cookies to determine who is signed in.

  2. A function to invoke when an onlogin action is triggered. This function is passed a single parameter, an “identity assertion,” which must be verified.

  3. A function to invoke when an onlogout action is triggered. This function is not passed any parameters.

Note: You must always include both onlogin and onlogout when you call navigator.id.watch().

For example, if you currently think Bob is logged into your site, you might do this:

var currentUser = 'bob@example.com';

navigator.id.watch({
  loggedInUser: currentUser,
  onlogin: function(assertion) {
    // A user has logged in! Here you need to:
    // 1. Send the assertion to your backend for verification and to create a session.
    // 2. Update your UI.
    $.ajax({ /* <-- This example uses jQuery, but you can use whatever you'd like */
      type: 'POST',
      url: '/auth/login', // This is a URL on your website.
      data: {assertion: assertion},
      success: function(res, status, xhr) { window.location.reload(); },
      error: function(xhr, status, err) {
        navigator.id.logout();
        alert("Login failure: " + err);
      }
    });
  },
  onlogout: function() {
    // A user has logged out! Here you need to:
    // Tear down the user's session by redirecting the user or making a call to your backend.
    // Also, make sure loggedInUser will get set to null on the next page load.
    // (That's a literal JavaScript null. Not false, 0, or undefined. null.)
    $.ajax({
      type: 'POST',
      url: '/auth/logout', // This is a URL on your website.
      success: function(res, status, xhr) { window.location.reload(); },
      error: function(xhr, status, err) { alert("Logout failure: " + err); }
    });
  }
});

In this example, both onlogin and onlogout are implemented by making an asynchronous POST request to your site’s backend. The backend then logs the user in or out, usually by setting or deleting information in a session cookie. Then, if everything checks out, the page reloads to take into account the new login state.

Note that if the identity assertion can't be verified, you should call navigator.id.logout(): this has the effect of telling Persona that none is currently logged in. If you don't do this, then Persona may immediately call onlogin again with the same assertion, and this can lead to an endless loop of failed logins.

You can, of course, use AJAX to implement this without reloading or redirecting, but that’s beyond the scope of this tutorial.

Here is another example, this time not using jQuery.

function simpleXhrSentinel(xhr) {
    return function() {
        if (xhr.readyState == 4) {
            if (xhr.status == 200){
                // reload page to reflect new login state
                window.location.reload();
              }
            else {
                navigator.id.logout();
                alert("XMLHttpRequest error: " + xhr.status); 
              } 
            } 
          } 
        }

function verifyAssertion(assertion) {
    // Your backend must return HTTP status code 200 to indicate successful
    // verification of user's email address and it must arrange for the binding
    // of currentUser to said address when the page is reloaded
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "/xhr/sign-in", true);
    // see http://www.openjs.com/articles/ajax_xmlhttp_using_post.php
    var param = "assertion="+assertion;
    xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xhr.setRequestHeader("Content-length", param.length);
    xhr.setRequestHeader("Connection", "close");
    xhr.send(param); // for verification by your backend

    xhr.onreadystatechange = simpleXhrSentinel(xhr); }

function signoutUser() {
    // Your backend must return HTTP status code 200 to indicate successful
    // sign out (usually the resetting of one or more session variables) and
    // it must arrange for the binding of currentUser to 'null' when the page
    // is reloaded
    var xhr = new XMLHttpRequest();
    xhr.open("GET", "/xhr/sign-out", true);
    xhr.send(null);
    xhr.onreadystatechange = simpleXhrSentinel(xhr); }

// Go!
navigator.id.watch( {
    loggedInUser: currentUser,
         onlogin: verifyAssertion,
        onlogout: signoutUser } );

You must call navigator.id.watch() on every page with a login or logout button. To support Persona enhancements like automatic login and global logout for your users, you should call this function on every page of your site.

Persona will compare the email address you've passed into loggedInUser with its own knowledge of whether a user is currently logged in, and who they are. If these don't match, it may automatically invoke onlogin or onlogout on page load.

 

Step 4: Verify the user’s credentials

Instead of passwords, Persona uses “identity assertions,” which are kind of like single-use, single-site passwords combined with the user’s email address. When a user wants to log in, your onlogin callback will be invoked with an assertion from that user. Before you can log them in, you must verify that the assertion is valid.

It’s extremely important that you verify the assertion on your server, and not in JavaScript running on the user’s browser, since that would be easy to forge. The example above handed off the assertion to the site’s backend by using jQuery’s $.ajax() helper to POST it to /auth/login.

Once your server has an assertion, how do you verify it? The easiest way is to use a helper service provided by Mozilla. Simply POST the assertion to https://verifier.login.persona.org/verify with two parameters:

  1. assertion: The identity assertion provided by the user.
  2. audience: The hostname and port of your website. You must hardcode this value in your backend; do not derive it from any data supplied by the user.

For example, if you’re example.com, you can use the command line to test an assertion with:

$ curl -d "assertion=<ASSERTION>&audience=https://example.com:443" "https://verifier.login.persona.org/verify"

If it’s valid, you’ll get a JSON response like this:

{
  "status": "okay",
  "email": "bob@eyedee.me",
  "audience": "https://example.com:443",
  "expires": 1308859352261,
  "issuer": "eyedee.me"
}

You can learn more about the verification service by reading The Verification Service API. An example /auth/login implementation, using Python, the Flask web framework, and the Requests HTTP library might look like this:

@app.route('/auth/login', methods=['POST'])
def login():
    # The request has to have an assertion for us to verify
    if 'assertion' not in request.form:
        abort(400)

    # Send the assertion to Mozilla's verifier service.
    data = {'assertion': request.form['assertion'], 'audience': 'https://example.com:443'}
    resp = requests.post('https://verifier.login.persona.org/verify', data=data, verify=True)

    # Did the verifier respond?
    if resp.ok:
        # Parse the response
        verification_data = json.loads(resp.content)

        # Check if the assertion was valid
        if verification_data['status'] == 'okay':
            # Log the user in by setting a secure session cookie
            session.update({'email': verification_data['email']})
            return 'You are logged in'

    # Oops, something failed. Abort.
    abort(500)

For examples of how to use Persona in other languages, have a look at the cookbook.

The session management is probably very similar to your existing login system. The first big change is in verifying the user’s identity by checking an assertion instead of checking a password. The other big change is ensuring that the user’s email address is available for use as the loggedInUser parameter to navigator.id.watch().

Logout is simple: you just need to remove the user’s session cookie.

Step 5: Review best practices

Once everything works and you’ve successfully logged into and out of your site, you should take a moment to review best practices for using Persona safely and securely.

If you're making a production site, have a look at the implementor's guide, where we've collected tips for adding the kind of features often needed in real-world login systems.

Lastly, don’t forget to sign up for the Persona notices mailing list so you’re notified of any security issues or backwards incompatible changes to the Persona API. The list is extremely low traffic: it’s only used to announce changes which may adversely impact your site.

 

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Last updated by: wbamberg,