identifierhere before the form is submitted.
OnBeginkey, you have to either return an error string, or return null if you want to continue the authentication process:
access_tokenthat you can send to your backend API to authorize a request. This access token contains the user's email or phone number. You should check if the email or phone number is allowed to log in in your backend server when validating the JWT token in addition to the OnBegin function.