notifier: smtp oauth2 credentials

Description

Currently, there are 2 methods to send notifications: filesystem and smtp. With smtp provider, if we want to connect to gmail, we need to set up an app password that can be used for purposes beyond just sending emails. It's a less secure option.

If we can setup oauth client and grant authelia sending email permission, it would be more secure.

Use Case

User setup gmail as notifier, authelia asks for sending email permission, user agrees and receives notification from email.

Details

No response

Documentation

OpenID Connect  |  Authentication  |  Google for Developers

Pre-Submission Checklist

• I agree to follow the Code of Conduct

• I have checked for related issues and checked the documentation