[Dovecot] CAS Authentication

[b m]

Hi.I'm very sorry for the repost but I forgot the subject.
So,  I'm 
using dovecot 2.0.18 and I'm trying to authenticate through a CAS server
 (until now authentication was through MS Active Directory). I could not
 find anywhere some examples, so here is what i have done so far.
-install phpcas and pam_cas
-edit /etc/pam.d/dovecot
                  auth    sufficient      /lib/security/pam_cas.so -simap://webmail.mydomain.com -f /etc/pam_cas.conf
-edit
 /etc.pam_cas.conf
                  host mycas.mydomain.com 
                  port 443 
                  uriValidate /cas/proxyValidate 
                  ssl on 
                  proxy ??????????????????????? 
                  trusted_ca /etc/cert/certificate.pem 
                  debug
 on

- and finally dovecot.conf which I'm sure is complety wrong
              userdb {
              args = /etc/dovecot/dovecot-ldap.conf
              driver = ldap
              }
             passdb {
             driver = pam
             args = cache_key=%u dovecot
             }

What I get in log is 


Oct 15 15:39:58 auth-worker: Debug: Loading modules from directory: /usr/lib64/dovecot/auth
Oct 15 15:39:58 auth-worker: Debug: Module loaded:
 /usr/lib64/dovecot/auth/libauthdb_ldap.so
Oct 15 15:39:58 auth-worker: Debug: Module loaded: /usr/lib64/dovecot/auth/libdriver_mysql.so
Oct 15 15:39:58 auth-worker: Debug: Module loaded: /usr/lib64/dovecot/auth/libdriver_pgsql.so
Oct 15 15:39:58 auth-worker: Debug: Module loaded: /usr/lib64/dovecot/auth/libdriver_sqlite.so
Oct 15 15:39:58 auth-worker: Debug: Module loaded: /usr/lib64/dovecot/auth/libmech_gssapi.so
Oct 15 15:39:58 auth-worker: Debug: pam(user,127.0.0.1): lookup service=dovecot
Oct 15 15:39:58 auth-worker: Debug: pam(user,127.0.0.1): #1/1 style=1 msg=Password: 
Oct 15 15:39:58 auth-worker: Info: pam(user,127.0.0.1): pam_authenticate() failed: Permission denied
Oct 15 15:40:00 auth: Debug: client out: FAIL    1    user=user
Oct
 15 15:40:00 imap-login: Info: Aborted login (auth failed, 1 attempts): 
user=<user>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured
Oct 15
 15:40:00 auth: Debug: auth client connected (pid=9019)

Any ideas? Thanks.