loginpage: Dataverse doesn't check whether DefaultAuthProvider is enabled or exists

This is user error to be certain and may become moot with the SPA, but since this behavior may be reproduced with API settings and was encountered today in version 5.13:

The :DefaultAuthProvider is documented on the configuration page, while AuthenticationProvider settings are documented on the Native API page. It is possible, when one needs to disable an authentication provider, to cause the other login options to disappear:

When the :DefaultAuthProvider setting points to an AuthenticationProvider which is disabled or has been deleted, Dataverse doesn't log an error to Payara's server.log or to the browser's Javascript console. Instead it simply doesn't generate the <div>. DefaultAuthProvider <id> has been disabled or deleted or some such may spare administrators a fair amount of troubleshooting.

Start at the login page handling for the :DefaultAuthProvider setting and reproduce the case where it names a disabled or deleted AuthenticationProvider. Check Payara's server.log and the browser JavaScript console while confirming the login options are missing. Done means the invalid provider condition produces a clear error such as “DefaultAuthProvider has been disabled or deleted.”