Author: Huong Nguyen
MDL-61921 admin: Support XOAUTH2 for incoming mail
http://git.moodle.org/gw?p=moodle.git;a=commit;h=986910d6ff8c19817c0c9b4addecc10b73d9157c
http://github.com/moodle/moodle/commit/986910d6ff8c19817c0c9b4addecc10b73d9157c
+ 4.1 en [messageinboundhostoauth_help,tool_messageinbound]