I've enabled both sql and oauth2 passdb, regardless of the method used by the client, I get the following error: Jan 1 15:38:56 mail dovecot[52828]: auth: Panic: file http-client.c: line 646 (http_client_context_close): assertion failed: (cctx->clients_list == NULL) Jan 1 15:38:56 mail dovecot[52826]: master: Error: service(auth): command startup failed, throttling for 2.000 secs Jan 1 15:38:56 mail dovecot[52828]: auth: Fatal: master: service(auth): child 52840 killed with signal 6 (core dumped) Jan 1 15:38:56 mail dovecot[52828]: imap-login: Disconnected: Auth process broken (disconnected before auth was ready, waited 0 secs): user=<>, rip=192.168.1.104, lip=192.168.1.101, TLS, session=<QW7rFYfUgcTAqAFo> If I remove the oauth2 passdb, there are no problems. This is the output of dovecot -n: # 2.3.17 (e2aa53df5b): /usr/local/etc/dovecot/dovecot.conf # Pigeonhole version 0.5.17 (054dddfa) # OS: FreeBSD 13.0-RELEASE-p4 amd64 nullfs # Hostname: localhost auth_mechanisms = plain login oauthbearer xoauth2 default_internal_user = vmail first_valid_uid = 0 hostname = ***DELETED*** mail_location = maildir:/data/mailboxes/%d/%n mail_plugins = " fts fts_solr" mail_privileged_group = vmail managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext namespace inbox { inbox = yes location = mailbox Archive { auto = subscribe special_use = \Archive } mailbox Drafts { auto = subscribe special_use = \Drafts } mailbox Junk { auto = subscribe special_use = \Junk } mailbox Sent { auto = subscribe special_use = \Sent } mailbox Trash { auto = subscribe special_use = \Trash } prefix = } passdb { args = /usr/local/etc/dovecot/dovecot-sql.conf.ext driver = sql } passdb { args = /usr/local/etc/dovecot/dovecot-oauth2.conf.ext driver = oauth2 mechanisms = xoauth2 oauthbearer } plugin { antispam_backend = pipe antispam_mail_notspam = learn_ham antispam_mail_sendmail = /usr/bin/rspamc antispam_mail_sendmail_args = -h;localhost:11334 antispam_mail_spam = learn_spam antispam_spam = Junk antispam_trash = Trash fts = solr fts_solr = url=http://localhost:8983/solr/dovecot sieve = ~/.dovecot.sieve sieve_before = /etc/dovecot/sieve/before.d sieve_dir = ~/sieve } postmaster_address = ***DELETED*** protocols = imap lmtp sieve pop3 service auth-worker { unix_listener auth-worker { user = vmail } } service auth { inet_listener { port = 1666 } unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0666 user = postfix } unix_listener auth-userdb { group = vmail mode = 0660 user = vmail } user = vmail } service imap-login { inet_listener imap { port = 0 } } service lmtp { inet_listener lmtp { port = 24 } unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0666 user = postfix } user = vmail } service pop3-login { inet_listener pop3 { port = 0 } } ssl = required ssl_cert =