Create some utility types/functions to help partners to create CasEncryptionRequest in JSON format and process CasEncryptionResponse in JSON format.

The idea is that partner can take the CasEncryptionRequest in JSON to construct a signed license request, send it to Widevine license service (using whatever tool they have); and once they have a response, they can use another utility here to parse and understand what is in the response JSON.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=229422648

media_cas_packager_sdk/public/wv_cas_types.h

@@ -10,6 +10,9 @@
 #define MEDIA_CAS_PACKAGER_SDK_PUBLIC_WV_CAS_TYPES_H_
 
 #include <string>
+#include <vector>
+
+#include "common/status.h"
 
 namespace widevine {
 namespace cas {
@@ -64,6 +67,63 @@ bool CryptoModeToString(CryptoMode mode, std::string* str);
 // Returns false if str is not a valid CryptoMode.
 bool StringToCryptoMode(const std::string& str, CryptoMode* mode);
 
+struct WvCasEncryptionRequest {
+  std::string content_id;
+  std::string provider;
+  // Track types such as "AUDIO", SD" or "HD".
+  std::vector<std::string> track_types;
+  // Indicates if the client is using key rotation.  If true, the server will
+  // return one key for EVEN and one key for ODD, otherwise only a single key is
+  // returned.
+  bool key_rotation = true;
+};
+
+struct WvCasEncryptionResponse {
+  enum class Status {
+    STATUS_UNSPECIFIED = 0,
+    OK = 1,
+    SIGNATURE_FAILED = 2,
+    ACCESS_DENIED = 3,
+    INTERNAL_ERROR = 4,
+    INVALID_ARGUMENT = 5,
+    PROVIDER_ID_MISSING = 6,
+    CONTENT_ID_MISSING = 7,
+    TRACK_TYPE_MISSING = 8
+  };
+  struct KeyInfo {
+    enum class KeySlot {
+      KEY_SLOT_UNSPECIFIED = 0,
+      SINGLE = 1,
+      EVEN = 2,
+      ODD = 3
+    };
+    std::string key_id;
+    std::string key;
+    // Optional label used for the key.
+    std::string track_type;
+    KeySlot key_slot;
+  };
+  Status status;
+  std::string status_message;
+  std::string content_id;
+  std::vector<KeyInfo> entitlement_keys;
+};
+
+// Returns a WvCasEncryptionRequest in JSON format.
+// This request JSON can be later put into the 'request' field of a signed
+// request JSON message.
+// And that signed JSON message can be sent to Widevine license server for
+// aquiring entitlement keys.
+Status CreateWvCasEncryptionRequestJson(const WvCasEncryptionRequest& request,
+                                        std::string* request_json);
+
+// Parses a WvCasEncryptionResponse in JSON format, returns a
+// WvCasEncryptionResponse.
+// |response_json| is supposed to be the 'response' field in the signed
+// response from Widevine license server.
+Status ParseWvCasEncryptionResponseJson(const std::string& response_json,
+                                        WvCasEncryptionResponse* response);
+
 }  // namespace cas
 }  // namespace widevine