LDAP

LDAP is the industry-standard protocol for accessing and managing distributed directory information services over an IP network.

Lightweight Directory Access Protocol (LDAP) functions as the structural backbone for enterprise identity management. It utilizes a hierarchical tree structure (the Directory Information Tree) to organize data like usernames, email addresses, and security groups. By operating on Port 389 (or 636 for LDAPS), it allows applications like OpenLDAP and Microsoft Active Directory to execute rapid lookups and authentication binds. Its efficiency stems from being optimized for high-volume read operations, making it the go-to choice for centralized credential storage across diverse corporate networks.

https://ldap.com/learn-about-ldap/