IMAP OAuth support

Problem to solve

Microsoft will stop support basic authentication for IMAP in 2021 2H, so GitLab e-mail fetching won't work on these addresses.

Intended users

Users who use Microsoft (and maybe Google) online e-mail systems.

Further details

https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-and-exchange-online-april-2020-update/ba-p/1275508

Proposal

Support OAuth for IMAP authentication.

Permissions and Security

Email replies

Documentation

• https://docs.gitlab.com/charts/installation/command-line-options.html#incoming-email-configuration
• https://docs.gitlab.com/ee/administration/incoming_email.html