Setting policies is the process of specifying conditions for when and how a user is allowed to play protected video content.
Policy creation occurs as part of your license token request. (See https://www.expressplay.com/developer/restapi/#widevine-license-token-request for an example using Widevine).
Once a customer’s server-side code has determined that it will issue a license (based on entitlements checks, geolocation, or any other required information), then it requests a token, and in the token it specifies the required
licenseDuration. Those are the client-side options for a Widevine policy. Other DRM solutions offer similar approaches, but the details are different in each case, and are elaborated upon in the individual workflows.
Adobe provides a sample reference server that shows how to implement your own entitlement server / storefront: Reference Server: Sample ExpressPlay Entitlement Server (SEES)