[Dovecot] CRAM-MD5 and proxy_maybe

Timo Sirainen tss at iki.fi
Thu Nov 20 03:20:41 EET 2008

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 = \
>    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  
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