Configure Cross-Origin Resource Sharing

Before you start

For security purposes, your application'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 application's Settings view is set to the domain making the request. The URLs can contain wildcards for subdomains, but 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 authentication.

Cross-origin resource sharing (CORS) is a mechanism that allows an application to load data (resource) from a domain (origin) that is different from the one that it's hosted on. A CORS policy is an explicit exception to the same-origin policy common to web applications.

For example, if you wanted your application (app.mydomain.com) to fetch a font from Google (fonts.google.com) in the background using Ajax, you would need to configure CORS.

Configure cross-origin authentication

Go to Dashboard > Applications > Applications and click the name of the application to view.
Under Cross-Origin Authentication, toggle on Allow Cross-Origin Authentication.
Locate Allowed Origins (CORS), and enter your application's origin URL. To learn more about Origins, read Origin on Mozilla MDN Web Docs.
Click Save Changes.

If you do not need to use CORS for your application, ensure that Allow Cross-Origin Authentication is toggled off.

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.

For browsers that are supported, you can use the crossOriginVerification method from the Auth0.js SDK in your application on a dedicated page to handle cases when third-party cookies are disabled.

For browsers that are not supported, such as Chrome, Opera, and Safari, cross-origin authentication will not work when third-party cookies are disabled unless you enable Custom Domains.

Safari's configuration is labeled as "Prevent cross-site tracking" and uses Intelligent Tracking Prevention. Unfortunately, this also prevents third-party cookies from being useful in authentication scenarios. Here's an example of how it affects token renewal.

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


<head>
  <script src="https://cdn.auth0.com/js/auth0/9.11/auth0.min.js"></script>
  <script type="text/javascript">
    var auth0Client = new auth0.WebAuth({
      clientID: '{yourClientId}',
      domain: '{yourDomain}'
    });
    auth0Client.crossOriginVerification();
  </script>
</head>
```
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When third party cookies are not available, Auth0.js renders an iframe to call a different cross-origin verification flow.
Go to Dashboard > Applications > Applications, and select the application to view.
Under Cross-Origin Authentication, add the URL of the callback page you created to the Cross-Origin Verification Fallback URL field.
For production environments, verify that the 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.
Click Save Changes.

For more details, view the cross-origin authentication sample on GitHub.

Error codes and descriptions

Error descriptions are intended to be human-readable. They are subject to change at any time and should not be parsed by any code.

When Auth0.js v9 (and Lock) is used for embedded login, it calls 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.
`400`	`unsupported_credential_type`	Unknown credential type parameter.
`400`	`invalid_request`	Unknown realm non-existent-connection.
`401`	`unauthorized_client`	Cross origin login not allowed.
`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).
`403`	`access_denied`	Wrong email or password.
`403`	`access_denied`	Authentication error
`403`	`blocked_user`	Blocked user
`429`	`too_many_attempts`	Your account has been blocked after multiple consecutive login attempts. We've sent you a notification via your preferred contact method 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 https://test.app is not allowed.

Browser testing support

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

Microsoft Internet Explorer

Samesite cookie attributes

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

Effective February 2020, Google Chrome v80 changed the way it handles cookies, and Auth0 implemented the following changes accordingly:

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 cross-site resource forgery (CSRF) attacks.

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