You need to have attributes populated on the users who will be in scope for being assigned access. The attributes you can use in the rules criteria of an access package assignment policy are those attributes listed in [supported properties](../identity/users/groups-dynamic-membership.md#supported-properties), along with [extension attributes and custom extension properties](../identity/users/groups-dynamic-membership.md#extension-attributes-and-custom-extension-properties). These attributes can be brought into Microsoft Entra ID by [patching](../identity/app-provisioning/user-provisioning-sync-attributes-for-mapping.md#create-an-extension-attribute-for-cloud-only-users-using-microsoft-graph) the [user](/graph/api/resources/user), an HR system such as [SuccessFactors](../identity/app-provisioning/sap-successfactors-integration-reference.md), [Microsoft Entra Connect cloud sync](../identity/hybrid/cloud-sync/how-to-attribute-mapping.md) or [Microsoft Entra Connect Sync](../identity/hybrid/connect/how-to-connect-sync-feature-directory-extensions.md). The rules can include up to 15,000 users per policy.