Hello,

I upgraded my servers from Debian Buster (v10) to Bullseye (v11). Before the upgrade, I had Roundcube / Dovecot working with LemonLdap (via OAuth).

After the upgrade, i can't connect to Roundcube anymore.

• roundcube (v1.5-rc) stayed the same
• Dovecot upgraded from v1:2.3.4.1-5+deb10u6 to v1:2.3.13+dfsg1-2

I already discussed on the LemonLdap mailing list and the analysis was: "Seems like your app is not sending client_id and client_secret correctly then It can do that either as POST parameters or in the Authorization header"

I downgraded Dovecot to Buster version (v1:2.3.4.1-5+deb10u6) and Roundcube / Dovecot are working again.

What could have change between these 2 versions to have that error?

My dovecot Oauth config:

debug = yes

## url for verifying token validity. Token is appended to the URL tokeninfo_url = https://auth.mydomain.name/oauth2/userinfo?access_token=

## introspection endpoint, used to gather extra fields and other information. introspection_url = https://auth.mydomain.name/oauth2/introspect

## How introspection is made, valid values are ## auth = GET request with Bearer authentication ## get = GET request with token appended to URL ## post = POST request with token=bearer_token as content introspection_mode = post

## TLS settings tls_ca_cert_file = /etc/ssl/certs/ca-certificates.crt

## username attribute in response (default: email) username_attribute = email

The error I found in the logs:

==> nginx/portal.log <== 11.22.33.44 - - [25/Oct/2021:16:31:59 +0200] "POST /oauth2/introspect HTTP/1.1" 401 355 "-" "dovecot-oauth2-passdb/2.3.13" -

==> error <== Oct 25 16:31:59 XXX LLNG[413575]: [error] No authentication provided to get token, or authentication type not supported

==> mail.log <== Oct 25 16:31:59 XXX dovecot[1390]: auth: Debug: http-client: conn 11.22.33.44:443 [12]: Got 401 response for request [Req72: POST https://auth.mydomain.name/oauth2/introspect]: Unauthorized (took 705 ms

• 0 ms in queue) Oct 25 16:31:59 XXX dovecot[1390]: auth: Error: oauth2(yyyyy@mydomain.name,127.0.0.1,): oauth2 failed: Object doesn't begin with '{'

Thanks, Kenny