[exim] ldap problem with AD trying SMTP AUTH

I'm using the following authenticator

server_condition = ${if ldapauth {\
                     user=${lookup ldapdn{LDAP_CRED \
                            ldap:///LDAP_BASE??sub?\
                            (sAMAccountName=${quote_ldap:$1})\
                           }{${quote_ldap_dn:$value}}fail} \
                     pass=${quote:$2} ldap:///}{yes}{no}}
      server_set_id = $1

(this was posted to the list a while back but is functionally
the same as one I wrote which fails in the same way)

I've experimented with quote_ldap_dn and quote_ldap and both fail with
the AD setup I'm using. The DN is found without problems but the
authentication step fails due to quoting issues it would seem...

The DN (from AD) has the form (I can't change it)

CN=Bloggs\, Fred,OU=....

Using quote_ldap, this becomes (on authentication)

CN=Bloggs\5C, Fred,OU=....

and fails, using quote_ldap_dn, I get

CN=Bloggs\\\, Fred\,OU=...

and that fails. I've used openldap 2.0.27 and openldap 2.2.24 libraries
with exim 4.68 with the same problem.

Does anyone have any ideas? I've looked through the list archive at
relevant posts.

Thanks very much.

-- 
Alan Thew                                       alan.thew@???
Computing Services, University of Liverpool     Fax: +44 151 794-4442