.. _authentication-proxies: ======================== Proxy PasswordDatabase ======================== Dovecot supports proxying IMAP, POP3, :ref:`submission_server`, :ref:`lmtp_server`, and :ref:`pigeonhole_managesieve_server` connections to other hosts. The proxying can be done for all users, or only for some specific users. There are two ways to do the authentication: 1. Forward the password to the remote server. The proxy may or may not perform authentication itself. This requires that the client uses only plaintext authentication, or alternatively the proxy has access to users' passwords in plaintext. 2. Let Dovecot proxy perform the authentication and login to remote server using the proxy's :ref:`authentication-master_users`. This allows client to use also non-plaintext authentication. The proxy is configured pretty much the same way as :ref:`authentication-host`, with the addition of proxy field. The common fields to use for both proxying ways are: * ``proxy`` and ``proxy_maybe``: Enables the proxying. Either one of these fields is required. * ``proxy_maybe`` can be used to implement ``automatic proxying``. If the proxy destination matches the current connection, the user gets logged in normally instead of being proxied. If the same happens with ``proxy``, the login fails with ``Proxying loops`` error. * ``proxy_maybe`` with LMTP require. * ``proxy_maybe`` with ``host=`` requires. * ``auth_proxy_self`` setting in ``dovecot.conf`` can be used to specify extra IPs that are also considered to be the proxy's own IPs. * ``proxy_always`` can be used with ``proxy_maybe`` to conditionally do proxying to specified remote host (host isn't self) or to let director assign a backend host (host is self). So basically this setting just always sends the ``proxy`` extra field to login process, but not necessarily the host. Useful when dividing users across multiple director clusters. * ``host=s``: The destination server's IP address. This field is required. * ``source_ip=s``: The source IP address to use for outgoing connections. .. versionadded:: v2.2.14 * ``port=s``: The destination server's port. The default is 143 with IMAP and 110 with POP3. * ``protocol=s``: The protocol to use for the connection to the destination server. This field is currently only relevant for LMTP: it can be used to select either ``lmtp`` or ``smtp``. * ``destuser=s``: Tell client to use a different username when logging in. * ``proxy_mech=s``: Tell client to use this SASL authentication mechanism when logging in. * ``proxy_timeout=`` <:ref:`time_msecs`>: Abort connection after this much time has passed. This overrides the default :dovecot_core:ref:`login_proxy_timeout`. .. versionchanged:: v2.3 Added support for milliseconds. * ``proxy_nopipelining``: Don't pipeline IMAP commands. This is a workaround for broken IMAP servers that hang otherwise. .. versionadded:: v2.2.11 * ``proxy_not_trusted``: ``IMAP/POP3`` proxying never sends the ``ID/XCLIENT`` command to remote. .. versionadded:: v2.2.27 You can use SSL/TLS connection to destination server by returning: * ``ssl=yes``: Use SSL and require a valid verified remote certificate. .. WARNING:: Unless used carefully, this is an insecure setting! Before v2.0.16/v2.1.beta1 the host name isn't checked in any way against the certificate's CN. The only way to use this securely is to only use and allow your own private CA's certs, anything else is exploitable by a man-in-the-middle attack. .. Note:: ssl_client_ca_dir or ssl_client_ca_file aren't currently used for verifying the remote certificate, although ideally they will be in a future Dovecot version. For now you need to add the trusted remote certificates to ssl_ca. .. Note:: LMTP proxying supports SSL/TLS only since v2.3.1 - for older versions any ssl/starttls extra field is ignored. .. Note:: doveadm proxying doesn't support SSL/TLS currently - any ssl/starttls extra field is ignored. * ``ssl=any-cert``: Use SSL, but don't require a valid remote certificate. * ``starttls=yes``: Use STARTTLS command instead of doing SSL handshake immediately after connected. * ``starttls=any-cert``: Combine starttls and ``ssl=any-cert``. Additionally you can also tell Dovecot to send SSL client certificate to the remote server using :dovecot_core:ref:`ssl_client_cert` and :dovecot_core:ref:`ssl_client_key` settings in dovecot.conf. Set :dovecot_core:ref:`login_trusted_networks` to point to the proxies in the backends. This way you'll get the clients' actual IP addresses logged instead of the proxy's. The destination servers don't need to be running Dovecot, but you should make sure that the Dovecot proxy doesn't advertise more capabilities than the destination server can handle. For IMAP you can do this by changing :dovecot_core:ref:`imap_capability` setting. For POP3 you'll have to modify Dovecot's sources for now ``(src/pop3/capability.h)``. Dovecot also automatically sends updated untagged CAPABILITY reply if it detects that the remote server has different capabilities than what it already advertised to the client, but some clients simply ignore the updated CAPABILITY reply. Source IPs ========== .. versionadded:: v2.2.14 If your proxy handles a lot of connections ``(~64k)`` to the same destination IP you may run out of TCP ports. The only way to work around this is to use either multiple destination IPs or ports, or multiple source IPs. Multiple source IPs can be easily used by adding them to the :dovecot_core:ref:`login_source_ips` setting in ``dovecot.conf``. You can also use hostnames which expand to multiple IPs. By prefixing the setting with ``?`` (e.g. ``login_source_ips = ?proxy-sources.example.com``) Dovecot will use only those IPs that actually exist in the server, allowing you to share the same config file with multiple servers. It's probably better not to include the server's default outgoing IP address in the setting, as explained here ``_. Disconnection delay =================== .. versionadded:: v2.2.19 To avoid reconnection load spikes when a backend server dies, you can tell proxy to spread the client disconnections over a longer time period (after the server side of the connection is already disconnected). :dovecot_core:ref:`login_proxy_max_disconnect_delay` setting in ``dovecot.conf`` controls this (disabled by default). Forwarding fields ================= .. versionadded:: v2.2.29 You can forward arbitrary variables by returning them prefixed with ``forward_``. Dovecot will use a protocol-dependent extension to forward these variables to the next hop. The next hop imports these to the auth request as passdb extra fields, so they are visible in e.g. ``%{passdb:forward_variable}``. If the proxying continues, all these fields are further forwarded to the next hop again. This feature requires that the sending host is in :dovecot_core:ref:`login_trusted_networks`. See :ref:`forwarding_parameters` for more details on how this is implemented for different protocols. Moving users between backends/clusters ====================================== .. versionadded:: v2.2.25 A safe way to move users from one cluster to another is to do it like: * Set ``delay_until=`` :ref:`authentication-password_database_extra_fields` where ```` is the current timestamp plus some seconds into future (e.g. 31s). You may also want to append e.g. +5 for some load balancing if a lot of users are moved at once. * Set ``host=`` :ref:`authentication-password_database_extra_fields`. This update should be atomic together with the ``delay_until`` field. * Use ``doveadm proxy kick`` or ``doveadm director kick`` to kick the user's existing connections. * The processes may still continue running in the backend for a longer time. If you want to be absolutely sure, you could also run a script to ``kill -9`` all processes for the user in the backend. This of course has its own problems. The idea here is that while the user's connections are being kicked and the backend processes are finishing up and shutting down, new connections are being delayed in the proxy. This delay should be long enough that the user's existing processes are expected to die, but not so large that clients get connection timeouts. A bit over 30 seconds is likely a good value. Once the ``delay_until`` timestamp is reached, the connections continue to the new host. If you have a lot of users, it helps to group some of them together and do the ``host/delay_until`` updates on a per-group basis rather than per-user basis. ID command forwarding ===================== .. versionadded:: v2.2.29 If you want to forward, for some reason, the IMAP ID command provided by the client, set .. code-block:: none imap_id_retain=yes This will also enable ``client_id`` variable in variable expansions for auth requests, which will contain the ID command as IMAP arglist. See :dovecot_core:ref:`imap_id_retain`. Password forwarding =================== If you don't want proxy itself to do authentication, you can configure it to succeed with any given password. You can do this by returning an empty password and ``nopassword`` field. Master password =============== This way of forwarding requires the destination server to support master user feature. The users will be normally authenticated in the proxy and the common proxy fields are returned, but you'll need to return two fields specially: * ``master=s``: This contains the master username (e.g. proxy). It's used as SASL authentication ID. * Alternatively you could return ``destuser=user*master`` and set ``auth_master_user_separator = *``. * ``pass=s``: This field contains the master user's password. See :ref:`authentication-master_users` for more information how to configure this. OAuth2 forwarding ================= If you want to forward :ref:`authentication-oauth2` tokens, return field ``proxy_mech=%m`` as extra field. Example password forwarding static DB configuration =================================================== See :ref:`authentication-static_password_database`. Example password forwarding SQL configuration ============================================= Create the SQL table: .. code-block:: none CREATE TABLE proxy ( user varchar(255) NOT NULL, host varchar(16) default NULL, destuser varchar(255) NOT NULL default '', PRIMARY KEY (user) ); Insert data to SQL corresponding your users. Working data could look like this: ====== ============= ================== user host destuser john 192.168.0.1 joe 192.168.0.2 joe@example.com ====== ============= ================== The important parts of ``dovecot.conf``: .. code-block:: none # If you want to trade a bit of security for higher performance, change these settings: service imap-login { service_count = 0 } service pop3-login { service_count = 0 } # If you are not moving mailboxes between hosts on a daily basis you can # use authentication cache pretty safely. auth_cache_size = 4096 auth_mechanisms = plain passdb { driver = sql args = /usr/local/etc/dovecot/dovecot-sql.conf.ext } The important parts of ``dovecot-sql.conf.ext``: .. code-block:: none driver = mysql connect = host=sqlhost1 host=sqlhost2 dbname=mail user=dovecot password=secret password_query = SELECT NULL AS password, 'Y' as nopassword, host, destuser, 'Y' AS proxy FROM proxy WHERE user = '%u' Example proxy_maybe SQL configuration ===================================== Create the SQL table: .. code-block:: none CREATE TABLE users ( user varchar(255) NOT NULL, domain varchar(255) NOT NULL, password varchar(100) NOT NULL, host varchar(16) NOT NULL, home varchar(100) NOT NULL, PRIMARY KEY (user) ); The important parts of ``dovecot.conf``: .. code-block:: none # user/group who owns the message files: mail_uid = vmail mail_gid = vmail auth_mechanisms = plain passdb { driver = sql args = /usr/local/etc/dovecot/dovecot-sql.conf.ext } userdb sql { driver = sql args = /usr/local/etc/dovecot/dovecot-sql.conf.ext } The important parts of ``dovecot-sql.conf.ext``: .. code-block:: none driver = mysql password_query = \ SELECT concat(user, '@', domain) AS user, password, host, 'Y' AS proxy_maybe \ FROM users WHERE user = '%n' AND domain = '%d' user_query = SELECT user AS username, domain, home \ FROM users WHERE user = '%n' AND domain = '%d' Example proxy LDAP configuration ================================ see: :ref:`authentication-password_database_extra_fields` for more information, and a worked out example .. toctree:: :maxdepth: 1 password_database_extra_fields static_password_database