[auth_oidc] Self-registration of users

[madduck]

Is your feature request related to a problem?

At the moment, to onboard a new user, the following steps are required:

1. Creation of user in the OIDC provider
2. Creation of equivalent user in Odoo, which sends them an email invitation
3. The user must accept the invitation
4. … and log in using SSO.

This is cumbersome and error-prone.

Describe the solution you'd like

When a user uses OIDC to log in to Odoo, and there is no corresponding user account, an Odoo user should be created on the fly, using data from the OIDC claims.

Ideally, I would be able to limit this "self-registration" to certain claim values, i.e. only allow users with email addresses matching e.g. *@example.org.

Additional context

WikiJS does this exceptionally well: