Identity Provider (explained)
Identity Provider app pool (IDP) is a system entity that creates, maintains, and manages identity information for basic users.
Identity Provider also provides authentication and registration services to relying applications or services, in this case: Recording Server, Management Server, Data Collector, and Report Server.
When you log in to XProtect clients and services as a basic user, your request goes to the Identity Provider. When authenticated the user can call the management server.
Identity Provider runs in the IIS as a part of the management server using the same SQL Server with a separate database and is responsible for creating and handling OAuth communication tokens that services use when communicating (Surveillance_IDP).
Identity Provider logs can be found at: \\ProgramData\Milestone\IDP\Logs.