With recent events, I decided to turn on 2-factor authentication for my Google mail. That worked fine. Then I set up application-specific passwords for Mail on my Mac, iPhone, and iPad, and Reeder ...

Their new authentication mechanism which they are calling XOAuth implements OAuth support for the IMAP and SMTP email protocols which traditionally do not support it.

I use courier-imap and I am currently using authdaemond (included with my courier-imap install) to do authentication.