PassKitSharp is a C#/.NET Library for Reading and Writing Apple PassKit files.
It's currently not complete, although the parser is working on a basic level. The parser currently does not check the signature, but does verify the hashes in the manifest.json for validity.
//Parse an existing pkpass file
var pk = PassKit.Parse("C:\\pass.pkpass");
Console.WriteLine(pk.Barcode.Message);
//Write a pkpass file out
pk.Write("C:\\passout.pkpass", "C:\\pass-cert.p12");