Configure oauth2 authentication for dovecot

[gderber]

References:

• https://doc.dovecot.org/configuration_manual/authentication/authentication_mechanisms/
• https://www.mail-archive.com/dovecot@dovecot.org/msg80830.html
• https://www.mail-archive.com/dovecot@dovecot.org/msg79305.html
• http://dovecot.2317879.n4.nabble.com/Dovecot-Xoauth2-keycloak-td71221.html#a71223
• https://doc.dovecot.org/configuration_manual/authentication/oauth2/
• https://wiki.dovecot.org/PasswordDatabase/oauth2
• https://www.howtoforge.com/postfix-dovecot-authentication-against-active-directory-on-centos-5.x
• https://docs.iredmail.org/active.directory.html
• https://doc.dovecot.org/configuration_manual/authentication/ldap/
• https://www.tcmlabs.com/index.php/2019/09/03/dovecot-xoauth2-keycloak-technote/

[gderber]

Blocked by #130

[gderber]

I have the basic structure for both Dovecot and Keycloak configured now. This feature isn't working.

I have noticed from the logs, that dovecot is not reading the username from the token. I have checked, it is in the token. I have also noticed, when I try to login, Dovecot does not appear to actually be contacting the keycloak server.

Something I have configured with one or the other is incorrect. I suspect it's something to do with the keycloak configuration because there is so much less documentation for how to setup the keycloak client for dovecot, than how to setup dovecot to use oauth2.