Apacheauth for svn, websvn, trac: internally show different name from logon name

We have a webserver which offers svn, websvn and trac using ApacheAuth, which we are in the process of moving to a new domain. I am looking for a way to have a translation Logonname -> Username.

This is why:

• For external reasons, the samAccountName is a 6-char string which is randomly assigned at account creation. This cannot be changed.
• In a collaboration context, it is preferrable to see a cleartext name.
• We have two persons with the same name, so the attribute displayName is problematic.
• Mail-Address is also problematic, because of the @ sign.
• We chose to use MailNickname, which proved to be unpopular with users, especially people with longer names. Also, for technical reasons, MailNickname is a bad choice, because it can change when users take a new mail alias.

Question:

In what way can I have people login using samAccountName, but display any other AD or LDAP attribute which is different from samAccountName, within svn, websvn, trac?

This is the Auth part of sites-available/svn:

    AuthType Basic
    AuthName "Username: your logon name"
    Require valid-user

    AuthLDAPBindDn CN=$account
    AuthLDAPBindPassword $password

    AuthBasicProvider ldap
    AuthzLDAPAuthoritative on
    AuthLDAPURL ldap://$server:389/$path?mailNickname?sub
    AuthLDAPGroupAttribute memberOf
    AuthLDAPGroupAttribute member
    AuthLDAPGroupAttributeIsDN on
    Require ldap-group CN=$groupname
    AuthzSVNAccessFile /srv/svn/auth/authz