LDAP

LDAP, the Lightweight Directory Access Protocol, is an open, vendor-neutral protocol for querying and modifying distributed directory information over an IP network. Directories hold hierarchical entries — people, groups, devices, and organizational units — keyed by distinguished names, and LDAP defines how clients bind, search, and update those entries. Standardized through the IETF (currently LDAPv3, RFC 4511) and dating to the early 1990s, it remains the backbone of enterprise identity behind systems like Active Directory and OpenLDAP.

• Hierarchical directory model - Entries organized as a tree of distinguished names with typed attributes.
• Bind and authentication - Simple and SASL binds that verify a user before any directory operation.
• Search and filter language - A compact filter syntax for locating entries by attribute across the tree.
• LDAPv3 over TLS - StartTLS and LDAPS protect credentials and directory traffic in transit.
• Schema and object classes - Definitions that constrain which attributes an entry may or must carry.

In API operations, LDAP is most often the identity source that authentication and authorization layers reach into rather than an API surface itself. API gateways, single sign-on, and management platforms validate users and resolve group memberships against an LDAP directory, then translate that identity into tokens for downstream calls. Modern estates increasingly wrap or replace direct LDAP access with OAuth and OIDC, but the directory underneath still governs who exists and what they belong to — making it foundational context even for agent-driven access decisions.