Entitlement rotation support

Updates also include:
- Add APIs to query current Simulcrypt channel & stream status;
- EMM format change (used only to carry fingerprinting and service
blocking info);
- Key fetcher example to use curl key fetcher.

protos/public/media_cas.proto

@@ -19,9 +19,8 @@ message CaDescriptorPrivateData {
   // Content ID.
   optional bytes content_id = 2;
 
-  // Entitlement key IDs for current content per track. Each track will allow up
-  // to 2 entitlement key ids (odd and even entitlement keys).
-  repeated bytes entitlement_key_ids = 3;
+  // Deprecated.
+  repeated bytes deprecated_entitlement_key_ids = 3;
 
   // The groups ids this channel belongs to.
   repeated bytes group_ids = 4;
@@ -78,6 +77,17 @@ message EcmMetaData {
   // Optional. The minimum age required to watch the content. The value
   // represents actual age, with 0 means no restriction.
   optional uint32 age_restriction = 2 [default = 0];
+  // If specified, it means entitlement key rotation is enabled. The value will
+  // be included in the license request. The server is expected to return
+  // entitlement keys accordingly (e.g., keys for |entitlement_period_index| and
+  // |entitlement_period_index| + 1).
+  optional uint32 entitlement_period_index = 3;
+  // Used only if entitlement key rotation is enabled. This parameter controls
+  // the probability of requesting a new license by clients upon receiving this
+  // ECM. The purpose is to spread out requests to avoid request storms. A
+  // client will request a new license with possibility = 1 /
+  // |entitlement_rotation_window_left|.
+  optional uint32 entitlement_rotation_window_left = 4 [default = 1];
 }
 
 message EcmKeyData {