OAUTH2 problem when migrating to Ubuntu 24.04

Hi,

I have a Dovecot server on Ubuntu 22.04, which works fine with Oauth2. I am building a new container based on Ubuntu 24.04. IMAP seems to work fine with plain authentication, but oauth2 fails (Dovecot v2.3.21). Same configuration as before.

However, I got this message:

May 09 09:41:57 auth: Error: oauth2(fran@mydomain.eu,10.110.41.32,): oauth2 failed: Introspection failed: No username returned

Weird, as it does indeed seems to get the username (as seen on the log).

Any clue on why this fails?

Best,

Francis