Proxying an insecure LDAP and authenticate using another

Hi!

I have a case where I got access to a read-only LDAP that has no authentication (everything is public). It is located in a secure and trusted environment. Now I want to expose the directory to another network and like to add authentication but can not add it to the source (proprietary software).

I need to proxy this server and authenticate the users using active directory.

I know how to proxy AD including passthrough authentication but can I proxy another directory and authenticate using another? If yes, how?

Thank you very much.

Kind regards Kevin Olbrich