Add support SSO

Hello, very much missing the ability to add authorization via the OIDC protocol for SSO to be able to make it possible to log in only via it

There is already Microsoft AAD OAuth support for the client portal. We could possibly add other providers if there was sufficient interest.

Federated login for technicians is trickier due to the way that client username/password credentials stored in ITFlow are encrypted.

Support for something like Authentik would be awesome.

There's an (unsupported) Docker build floating around that would allow this.