A license server (also called a key server) is the service that issues the decryption key and usage policy to an authorized player so it can play protected content. It is the enforcement point of DRM: encryption locks the content, but the license server decides — per request, per user, per device — whether to hand over the key and under what rules.
The flow: the player obtains a license challenge from its DRM module and sends it to the license server; the server authenticates the user, checks entitlement (is this account allowed to watch this title right now?), and, if approved, returns the content key bound to the device plus policy — output protection requirements, license expiry, offline/rental duration, HDCP level. The key is delivered into the device's secure decryption module, never exposed to application code.
Because it gates every protected playback, the license server must be highly available and low-latency (it is in the startup path), scale with concurrency, and integrate tightly with the entitlement and billing systems. In multi-DRM it speaks Widevine, PlayReady, and FairPlay behind one endpoint.
