auth_debug                      = yes
auth_debug_passwords            = yes

auth_ssl_require_client_cert    = yes
auth_ssl_username_from_cert     = yes

auth_mechanisms                 = plain external

passdb {
    driver              = passwd-file
    args                = scheme=PLAIN username_format=%u /etc/dovecot/users
    mechanisms          = plain external
    override_fields     = nopassword
}

userdb {
    driver              = passwd-file
    args                = /etc/passwd
}