The git repository contains new support for the OAUTHBEARER authentication method, formerly known as XOAUTH2, a method pushed mainly by Google.
This means msmtp can now use an OAuth2 token for authentication by setting auth oauthbearer in the configuration file. The token is typically passed to msmtp via the passwordeval command since it changes regularly.
However, msmtp does not provide a way to generate such a token. This depends on your mail provider.
Since I do not use this method myself, it would be great if you could test this feature and maybe document how to generate the necessary token for your mail provider, so that I can add examples to the documentation.
Looking forward to your feedback!