Add support for Office 365 smtp online exchange using SASL XOAUTH2

[HanoRossouw]

We tried during our setup to configure Office 365 for sending mails via the cloud service but apparently they are moving away from basic auth and moving to oauth based smtp security (https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-retire-basic-auth-for-client-submission-smtp-auth/4114750)

they have documentation on their new way of authenticating which might be implemented by other email vendors in near future as they move away from basic auth with smtp

https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth#authenticate-connection-requests

This requires adding support for SASL XOAUTH2

AUTHENTICATE XOAUTH2
and the format is
base64("user=" + userName + "^Aauth=Bearer " + accessToken + "^A^A")