Embedded Passwordless Authentication for SPAs
Embedded login for web uses Cross Origin Authentication. In some browsers this can be unreliable if you do not set up a Custom Domain and host your app on the same domain. If you cannot use Custom Domains, consider migrating to Universal Login.
Using Auth0's SDKs to implement Embedded Login
You can implement Passwordless Login using Auth0's Lock widget, or if you need complete control of the user experience, you can implement it using Auth0.js:
Configure Cross-Origin Resource Sharing (CORS)
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).
Navigate to Auth0 Dashboard > Applications > Applications, and select the name of your application to see its settings.
Locate Allowed Origins (CORS), enter your application's origin URL, and select Save Changes.