Some software publishers define that access to server software requires licenses for corresponding users or devices. This is called "Client Access Licensing" (CAL). The major difference to licensing for applications is, that the subject of licensing is a theoretical software product. It cannot be installed and thus, measuring required licenses is quite different and sometimes becomes quite difficult.
Approaching a procedure to achieve automatic measurement requires to understand how the corresponding publisher defines the prerequisites and conditions for a license requirement. As a matter of fact, there is no common definition for all cases. Therefore, it is required to find a solution for every single CAL product.
User vs. device access
Software publishers usually provide options to license CAL per named user or per named device. But there are variations. Some vendors limit CAL to "per named user", others include automated (user-less) devices into the "per user" licensing.
In any case it is important to understand the conditions that trigger the license requirement. It must be clear, that software publishers usually understand "client access" as a theoretical concept of "somehow" using the backend server or service. In common software and infrastructure architectures this could be rather indirect which means that there is not direct connection from the using end-point device to the server or service. For instance, Client-Server applications usually form a "black box" where the user connects to a business application only, while the database used to store all data may is accessed from a central system account (Multi-Plexing). Nevertheless, every user or end-point device using the business application may require a CAL for the database.
There are different options to automate creation of license requirements, depending on the trigger condition and available technical usage data.
If the trigger is based on Remote Desktop access, it is recommended to deploy "Remote Usage Tracking Agent" and configure the corresponding CAL software product. The system will then use the tracking data of measured connections to create and maintain license requirements (e.g. for Remote Desktop Services CAL).
Active Directory group
In case the trigger is based on access rights or roles, the corresponding AD group can be assigned to the CAL software product. The system will then use the memberships of that group to create and maintain license requirements (e.g. Windows Server CAL).
License requirement rules
If the CAL is required as a side-effect of using other software, a rule can be defined to create requirements for it based on license requirements for other software. The system will then use the rule to create and maintain license requirements (e.g. Exchange CAL, SQL Server CAL).