proposal: net/smtp: add SASL XOAUTH2 authentication

[drakkan]

Proposal Details

Microsoft and Google seems to force the switch from Basic authentication to SASL XOAUTH2:

https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth
https://developers.google.com/gmail/imap/xoauth2-protocol

Implementing the protocol is quite simple, maybe we can add it to the standard library

[gopherbot]

Change https://go.dev/cl/550535 mentions this issue: net/smtp: add SASL XOAUTH2 authentication

[mateusz834]

I don't want to stop this kind of change, but currently the package docs says that:

The smtp package is frozen and is not accepting new features. Some external packages provide more functionality.

Also is seems like XOAUTH2 does not have an RFC and iana considers it as obsolete for some reason: https://www.iana.org/assignments/sasl-mechanisms/sasl-mechanisms.xhtml

[drakkan]

@mateusz834 Thank you. You're right, I've already added XOAUTH2 to an external package (go-mail). I didn't notice the note in the package documents. I'm sorry for the noise