I don’t see why not. Zeroshell uses freeradius which supports proxy and ldap integration.
You will need to do some editing in freeradius to get it to work though.
Go into radiusd.conf and edit with vi or emacs and look for the statements that say LDAP in it fill them in and uncomment as necessary.
server = FQDN for your server or IP address
login = ldap login looks like cn=?,o=?,c=?
password = ldap password
basedn = ou=?,dc=?,dc=?
look for any other sections for ldap that say to uncomment to make it work.
Then edit your dictionary.conf, make sure a Value of LDAP IS PRESENT if not add it in or uncomment it.
Then in users.conf add the default entry for
Auth-Type =: LDAP
Fall-Through = 1
If your ldap server is ready to serve requests then that’s all you need to authenticate. Restart freeradius service and then zeroshell should be checking with the ldap server for credentials.