When a user registers an account on the community, your handler can check if the email address or username is acceptable. This is useful if you want your login handler to provide close integration such as is provided by the LDAP and IPS Connect handlers. The methods are emailIsInUse() and usernameIsInUse().
$email (string, required)
The email address to check
$exclude (\IPS\Member, optional)
If provided, excludes the supplied member from the check for uniqueness
$username (string, required)
The username to check