CiviCRM contacts are identified by their CiviCRM ID and, optionally, an external identifier, which is a single-calue filed on Contact entities.
This extension provides means for keeping track of multiple identifiers of different configurable types for Contact entities by adding a multi-value custom field group and an API for easily identifying contacts by those ID records.
Warning
Incompatible with CiviCRM Core 5.71 prior to version 1.4
The extension is incompatible with CiviCRM Core starting from version 5.71.0
due to misuse of the API internally (which actually worked by accident).
Identity Tracker version 1.4 fixes this incompatibility.