Use SimpleLogin's oauth as authentication method

[ZeroTricks]

https://proton.me/blog/sso-integration
https://simplelogin.io/docs/siwsl/intro/
https://app.simplelogin.io/.well-known/openid-configuration/
https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/47641541-proton-identity-sso-idp
https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/40659877-sign-in-log-in-with-proton-like-oauth-2-0

Research:

• Does it work (smoothly) for Proton users who don't use SimpleLogin?
• Can we get all necessary tokens & keys (refresh & userkey) via this method? (for basic Lumo access)
• If yes, give these tokens the 'lumo' scope for conversation sync? (see Support conversation sync on "login" auth method #3)

If yes, this should be the recommended way to login:

• no handling of user credentials
• users are probably familiar with auth flow, even if setting up callback can take some effort