Allow for private or invite-only registration #402
Description
Some registries prefer having a private mechanism for registering users. The idea is that we will generate a secret token used for accessing the /registration endpoint.
Once a user has been registered, the token will be destroyed.
Tokens could be tied to a registration email, preventing one from using a token against a different email address.
Administrators would have the ability to invite users based on a list of email addresses.
Users could also have the ability to invite other users, though on a one-by-one basis.
- add a configuration option to make registration private (or invite-only)
- hide registration links from the login page and other places
- add an admin section to generate registration tokens & links
- add a mechanism for sending invite emails with a template message
- allow registered users to create invitation links