Limited account creation (shownewaccount=1) to invited users or whitelisted domains.

Option to Enable/disable a user account creation whitelist.

This whitelist will be automatically filled by inviting users on share creation, and the entry will be removed after account creation, and the possibility to add whole domains to the whitelist manually.

For example: I can manually add *@contosocorp.com which means anyone from that domain can create an account using the account creation page. Other then the invited users any other email-address used to create an account will be blocked.