Shared Mailboxes in Dovecot Cluster & director configuration

[Markus Valentin]

> On 08/06/2021 13:46 Vincent Brillault <vincent.brillault at cern.ch> wrote:
> 
>  
> Hi!
> 
> I've been trying to set a shared namespace on a test dovecot cluster and
> I've had some weird issues. I'm not sure if this is a feature or a bug,
> so please advice.
> 
> As some features (like acl_ignore_namespace) are only in the upcoming
> 2.3.15, after some initial debugging, I've update the system I'm using
> to the master branches (df1b4b8750fdb87d38ac9accb8a1dea02ac3ce2e for
> core and 7090e62564bcb7bff7efc89bd2a42b1d32d9e475 for pigeonhole), but
> it didn't change the initial issues I was having.
> 
> I've been following
> https://doc.dovecot.org/configuration_manual/shared_mailboxes/cluster_setup/
> and linked documentations to set up the cluster. You'll find at the end
> of the mail the parts of the configuration that seems to be relevant.
> 
> The issues I've had was with the `You’ll need to setup master user
> logins to work for all the users.` and `imapc_master_user` (for which
> the bullet points recommend to use `%{userdb:sharing_user}` but is then
> set to `%u` in the example.
> 
> For the sake of the tests, I'm using one director and one backend. On
> this installation:
> - user1 shared the folder 'Junk' with user2
> - after logging as user2, I run `a2 SELECT shared/user1/Junk`
> 
> Initially on the director, I had (excluding other, unrelated configuration):
> ```
> # Connection back from backends for shared mailbox access
> passdb {
>   args = password=XXXX allow_nets=${IPs of backend}
>   driver = static
>   master = yes
>   mechanisms = plain
>   result_success = continue
> }
> ```
> 
> However, this lead to login failures on the director as the backend was
> logging directly as user1, without master user set!
> 
> After further debugging, I now have on the director:
> ```
> # Connection back from backends for shared mailbox access
> passdb {
>   args = password=XXXX allow_nets=${IPs of backend}
>   driver = static
>   master = yes
>   mechanisms = plain
>   result_success = continue
> }
> passdb {
>   args = password=XXXX allow_nets=${IPs of backend}
>   driver = static
>   mechanisms = plain
>   result_success = continue
> }
> ```
> 
> And this works! Looking at the log, it's not that my `imapc_master_user`
> is not recognized, just that there are two imapc connections from the
> backend to the frontend.
> - The first one logs as user1 directly, with no master user set:
>   ```
>   ${backend} dovecot[29900]: imap(user2)<29917><Mi/7WD/EgYi8uE1E>:
> Debug: imapc(${director}:993): Authenticating as user1
>   ```
> - The second connection logs as expected, as user1 with user2 set as the
> master user:
>   ```
>   ${backend} dovecot[29900]: imap(user2)<29917><Mi/7WD/EgYi8uE1E>:
> Debug: imapc(${director}:993): Authenticating as user2 for user user1
>   ```
> 
> Is it normal to have these two connections back to the director? From
> the documentation, I would have only expected the 2nd one.
> 
> 
> Going further, if I add a static part to imapc_master_user, like for
> example `imapc_master_user = X%{userdb:sharing_user}`, the logged
> authentications become:
> ```
> ${backend} dovecot: imap(user2)<31073><xu94pz/EqYi8uE1E>: Debug:
> imapc(${director}:993): Authenticating as X for user user1
> [...]
> ${backend} dovecot: imap(user2)<31073><xu94pz/EqYi8uE1E>: Debug:
> imapc(${director}:993): Authenticating as Xuser2 for user user1
> ```
> 
> It looks to me that for the first connection, imapc_master_user is
> resolved with the wrong context, without `userdb:sharing_user` resolving
> to anything?

Hi,

thank you very much for the details and sending feedback.

I am sorry there have been bugs in the documentation. The two connections are expected but the missing master_user for the first connection is a problem. The documentation suggested a not so greatly working way of doing it.

It works better if the backend userdb or passdb sets imapc_master_user=%{user} or userdb_imapc_master_user=%{user}. 

The userdb_sharing_user was meant to make it easier and better readable but made it more complicated and nonfunctional, sorry.

The documentation will be updated soon. There will be also some example configuration snippets to make it easier to configure.

Markus

> 
> 
> Thanks in advance, let me know if you need more details.
> Vincent Brillault
> 
> 
> PS configuration details (relevant parts of doveconf -n):
> - Backend:
> ```
> auth_master_user_separator = *
> imapc_features = fetch-bodystructure fetch-headers rfc822.size search modseq
> imapc_host = ${director}
> imapc_master_user = %{userdb:sharing_user}
> 
> imapc_password = # hidden, use -P to show it
> imapc_port = 993
> imapc_sasl_mechanisms = plain
> imapc_ssl = imaps
> imapc_ssl_verify = no
> mail_plugins = acl zlib virtual fts fts_solr
> namespace {
>   list = children
>   location = imapc:~/shared/%%u
>   prefix = shared/%%u/
>   type = shared
> }
> namespace Virtual {
>   hidden = yes
>   list = no
>   location = virtual:/etc/dovecot/virtual:INDEX=~/virtual
>   prefix = Virtual/
>   separator = /
>   subscriptions = no
> }
> namespace inbox {
>   inbox = yes
>   location =
>   mailbox "Deleted Items" {
>     auto = subscribe
>     special_use = \Trash
>   }
>   mailbox Drafts {
>     auto = subscribe
>     special_use = \Drafts
>   }
>   mailbox "Sent Items" {
>     auto = subscribe
>     special_use = \Sent
>   }
>   mailbox Spam {
>     auto = create
>     special_use = \Junk
>   }
>   prefix =
> }
> passdb {
>   args = password=#hidden_use-P_to_show# allow_nets=${IPs of director}
> userdb_namespace/shared/disabled=yes
>   driver = static
>   master = yes
> }
> passdb {
>   args = password=#hidden_use-P_to_show# allow_nets=${IPs of director}
> userdb_sharing_user=%u
>   driver = static
> }
> plugin {
>   acl = vfile:/etc/dovecot/dovecot-acl
>   acl_ignore_namespace = Virtual/
>   acl_ignore_namespace2 = shared/*
>   acl_shared_dict = file:/mail/sharing/shared-mailboxes
>   [...]
> }
> ```
> - Director (final & working version):
> ```
> auth_master_user_separator = *
> auth_mechanisms = plain login xoauth2 oauthbearer gssapi
> auth_socket_path = director-userdb
> passdb {
>   args = /etc/dovecot/passdb-masterusers.conf.ext
>   driver = ldap
>   master = yes
>   mechanisms = plain login
>   result_success = continue
> }
> passdb {
>   args = password=#hidden_use-P_to_show# allow_nets=${IPs of backend}
>   driver = static
>   master = yes
>   mechanisms = plain
>   result_success = continue
> }
> passdb {
>   args = password=#hidden_use-P_to_show# allow_nets=${IPs of backend}
>   driver = static
>   mechanisms = plain
>   result_success = continue
> }
> passdb {
>   args = /etc/dovecot/passdb-oauth2.conf.ext
>   driver = oauth2
>   mechanisms = xoauth2 oauthbearer
>   result_failure = return-fail
>   result_internalfail = return-fail
>   result_success = continue
> }
> passdb {
>   args = /etc/dovecot/passdb-cerndc.conf.ext
>   driver = ldap
> }
> ```