Configure Cross-Origin Resource Sharing

Configure Cross-Origin Resource Sharing

Auth0 strongly recommends that authentication transactions be handled via Universal Login. Doing so offers the easiest and most secure way to authenticate users. However, some situations may require that login be directly embedded in an application. When embedded login is required, an application must be set up for cross-origin resource sharing (CORS).

You can configure CORS for an application using the Auth0 Dashboard.


  • For security purposes, your app's origin URL must be listed as an approved URL. If you have not already added it to the Allowed Callback URLS for your application, you will need to add it to the list of Allowed Origins (CORS).

  • Ensure that Allowed Web Origins in your applications Settings tab is set to the domain making the request. The URLs can contain wildcards for subdomains and cannot contain relative paths after the domain URL. To learn more, read Placeholders for Subdomains.

  • If you don't enable Custom Domains, you will need to create a verification page that uses Auth0.js as the fallback for the cross-origin transaction.

Configure cross-origin authentication

  1. Go to Dashboard > Applications > Applications and click the name of the application to view.

  2. Under Application URIs, locate Allowed Origins (CORS), enter your app's origin URL.

    Dashboard Applications Application Settings Application URIs

    To learn more about the origin request header, read Origin request header at

  3. Click Save Changes.

Create cross-origin verification page

There are some cases when third-party cookies will not be available. Certain browser versions do not support third-party cookies and, if they do, they may be disabled in a user's settings. You can use Auth0.js in your application on a dedicated page to handle cases when third-party cookies are disabled. This page must be served over SSL.

Using crossOriginVerification as a fallback will only work if the browser is on the support matrix as Yes under Third-Party Cookies Disabled. For some browsers, such as ChromeOpera, and Safari, when third-party cookies are disabled, cross-origin authentication will not work at all unless you enable Custom Domains.

  1. Create a page in your application that instantiates WebAuth from Auth0.js. Call crossOriginVerification immediately. The name of the page is up to you.

    <!-- callback-cross-auth.html -->
      <script src=""></script>
      <script type="text/javascript">
        var auth0Client = new auth0.WebAuth({
          clientID: '{yourClientId}',
          domain: '{yourDomain}'

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    When third party cookies are not available, Auth0.js renders an iframe to call a different cross-origin verification flow.

  2. Go to Dashboard > Applications > Applications and select your application and click Advanced Settings at the bottom of the page.

  3. On the OAuth tab, add the URL of the callback page you created to the Cross-Origin Verification Fallback field. For production environments, verify that the Location URL for the page does not point to localhost. The page must be in the same domain where the embedded login form is hosted and must have an https scheme.

  4. Click Save Changes.

See the cross-origin auth sample HTML in GitHub for more details.

Error codes and descriptions

When Auth0.js v9 (and Lock v11) is used for embedded login, it employs the /co/authenticate endpoint, which has the following errors.

Status Code Description
400 invalid_request Invalid request body. All and only of client_id, credential_type, username, otp, realm are required.
401 unauthorized_client Cross origin login not allowed.
400 unsupported_credential_type Unknown credential type parameter.
400 invalid_request Unknown realm non-existent-connection.
403 access_denied Wrong email or password.
403 access_denied Authentication error
403 blocked_user Blocked user
401 password_leaked This login attempt has been blocked because the password you're using was previously disclosed through a data breach (not in this application).
429 too_many_attempts Your account has been blocked after multiple consecutive login attempts. We’ve sent you an email with instructions on how to unblock it.
429 too_many_attempts We have detected suspicious login behavior and further attempts will be blocked. Please contact the administrator.

In addition, you can also get a generic 403 error without an error or error_description property. The response body would just include something similar to the following:

Origin is not allowed.

Browser testing support

The following browsers can use cross-origin authentication when third-party cookies are disabled:

  • Microsoft Internet Explorer

  • Microsoft Edge

Samesite cookie attributes

Previously in Auth0, the samesite cookie attribute options were truefalsestrict or lax. If you didn't set the attribute manually, Auth0 would use the default value of false.

Effective February 2020, Google Chrome v80 will change the way it handles cookies. To that end, Auth0 plans on implementing the following changes to how it handles cookies:

  • Cookies without the samesite attribute set will be set to lax

  • Cookies with sameSite=none must be secured, otherwise they cannot be saved in the browser's cookie jar

The goal of these changes are to improve security and help mitigate CSRF attacks.

Learn more