If I understand your requirement correctly, you are trying to implement Custom LDAP authentication for your Pega Application. If that is the case, you can go through the following help documentation link to configure Custom authentication via an external Active Directory / LDAP Server.
Unfortunately current versions of the PRPC Platform do not have Out-of-the-box REST Connectors to connect to AD/LDAP. However, you should be able to quickly leverage the Connect REST rules to invoke AD/LDAP REST Services. You can consult the vendor's REST API documentation in order to instrument the Connect REST rules.