The Jwt code was dropped somewhere in a merge. Put it back

include/grpc++/credentials.h

@@ -105,6 +105,14 @@ std::unique_ptr<Credentials> ServiceAccountCredentials(
     const grpc::string& json_key, const grpc::string& scope,
     std::chrono::seconds token_lifetime);
 
+ // Builds JWT credentials.
+  // json_key is the JSON key string containing the client's private key.
+  // token_lifetime is the lifetime of each Json Web Token (JWT) created with
+  // this credentials.  It should not exceed grpc_max_auth_token_lifetime or
+  // will be cropped to this value.
+std::unique_ptr<Credentials> JWTCredentials(
+    const grpc::string& json_key, std::chrono::seconds token_lifetime);
+
 // Builds IAM credentials.
 std::unique_ptr<Credentials> IAMCredentials(
     const grpc::string& authorization_token,

src/cpp/client/secure_credentials.cc

@@ -104,6 +104,15 @@ std::unique_ptr<Credentials> ServiceAccountCredentials(
       json_key.c_str(), scope.c_str(), lifetime));
 }
 
+// Builds JWT credentials.
+std::unique_ptr<Credentials> JWTCredentials(
+    const grpc::string &json_key, std::chrono::seconds token_lifetime) {
+  gpr_timespec lifetime = gpr_time_from_seconds(
+      token_lifetime.count() > 0 ? token_lifetime.count() : 0);
+  return WrapCredentials(
+      grpc_jwt_credentials_create(json_key.c_str(), lifetime));
+}
+
 // Builds IAM credentials.
 std::unique_ptr<Credentials> IAMCredentials(
     const grpc::string& authorization_token,