An LDAP server providing authentication services to the cardholder data environment is

An LDAP server is a type of directory service that provides authentication and authorization data to the cardholder data environment (CDE)1. According to the PCI DSS scoping and segmentation guidance2, any system that provides a security service to the CDE, such as authentication, is considered a connected or security-impacting system (Category 2) and is in scope for PCI DSS. This is because such systems can affect the security and controls of the CDE and the cardholder data (CHD) or sensitive authentication data (SAD) that it contains. Therefore, an LDAP server providing authentication services to the CDE is in scope for PCI DSS, regardless of whether it stores, processes, or transmits CHD or SAD, or whether it provides authentication services to systems in the DMZ or not. References:

Guidance for PCI DSS Scoping and Network Segmentation

What Are the Effects of Using Active Directory as a Shared Service on PCI Compliance?

The Ultimate Guide To PCI DSS Scoping and Segmentation

LDAP - PCI Security Standards Council