[Dovecot] CRAM-MD5 and proxy_maybe

[David Jonas]

Timo Sirainen wrote:
> On Nov 19, 2008, at 8:14 PM, David Jonas wrote:
>
>> When using proxy_maybe CRAM-MD5 authentication fails when the connection
>> is proxied. Is this expected behavior? Is proxy_maybe too simplified for
>> this case?
>
> Fails how?
>
>> We're using SQL so I could rewrite the query with IFs to fake
>> proxy_maybe and return the password as NULL and nologin as Y, but if it
>> works that way couldn't it work with proxy_maybe?
>>
>> This works:
>>
>> password_query = \
>>  SELECT NULL AS password, host, CONCAT(user,'@',domain) AS destuser \
>>    'Y' AS nologin, 'Y' AS nodelay, 'Y' AS proxy \
>>  FROM accounts WHERE class='pop' AND domain='%d'
>
> So all servers are using this authentication? It works because it lets
> users log in using any password.
>
>> This doesn't work if proxied and CRAM-MD5 auth:
>>
>> password_query = \
>>  SELECT \
>>    CONCAT(user,'@',domain) AS user, password, \
>>    host, 'Y' AS proxy_maybe, \
>>    target AS userdb_home, uid AS userdb_uid, gid AS userdb_gid \
>>  FROM accounts
>>  WHERE \
>>    class='pop' AND domain='%d' AND user='%n' \
>>  LIMIT 1
>
>
> The problem is that Dovecot doesn't know the plaintext password for
> logging into the remote server. It can't be extracted from CRAM-MD5
> authentication. Are you storing plaintext passwords in the "password"
> field? If so, you could return "password as pass" (as well as the
> password field itself). If you're not using plaintext passwords,
> you'll have to use a master password (see
> http://wiki.dovecot.org/PasswordDatabase/ExtraFields/Proxy).
>
> (I suppose in theory Dovecot could also implement CRAM-MD5 client
> functionality and use the stored CRAM-MD5 hash to log into the remote
> server, but this wouldn't work with many other auth mechanisms, such
> as DIGEST-MD5, so I don't want waste time on coding a CRAM-MD5-only
> solution.)
Thanks Timo. I've been playing with the query for the past few hours and
I have a workable solution which turns out to be what you suggested
(passing "pass") since we have to store plaintext anyway. It took me
awhile to glean it from the docs. Thanks for the support. We really
appreciate it.

Here's our query, for posterity:

  SELECT \
    IF('%l' != host, host, NULL) AS host, \
    IF('%l' != host, 'Y', NULL)  AS proxy, \
    IF('%l' != host, 'Y', NULL)  AS nodelay, \
    IF('%l' != host, 'Y', NULL)  AS nologin, \
    IF('%l' != host, "%n@%d", NULL)  AS destuser, \
    IF('%l' != host, password, NULL) AS pass, \
    CONCAT(user,'@',domain) AS user, \
    password, \
    target AS userdb_home, uid AS userdb_uid, gid AS userdb_gid \
  FROM accounts
  WHERE \
   class='pop' AND domain='%d' AND user='%n' \
  LIMIT 1