如何在dotnet中验证JWS？

Question

遇到一个困扰我很久的问题，查了很多资料，但大多只是Java和PHP的。然而，事实证明，将此代码移植到 .NET 非常具有挑战性。

要求

我正在开发一个iOS应用程序，需要与Apple应用内购买（IAP）系统集成。用户成功购买后，Apple服务器会生成回调并向我发送一串信息，我需要验证这些信息的真实性。但我不知道该怎么做。 （虽然我很想分享这个JWS的内容，但它包含敏感信息，不能公开披露。）

目前进展

1. 回调信息验证:

   • 回调中发送的信息是 JSON 字符串，其中负载是 JWS。这个JWS可以直接在https://jwt.io进行验证，确认JWS是有效的并且可以自我验证。

2. 证书链验证:

   • 我可以使用

     X509Chain

     类来验证 JWS

     x5c

     部分中的证书链。这是我的验证码：

   // AppleRootCA-G3.cer is downloaded from apple.com manually 
   var AppleRootCA = new X509Certificate2("AppleRootCA-G3.cer");
   var handler = new JwtSecurityTokenHandler();
   var jsonToken = handler.ReadToken(dto.signedPayload) as JwtSecurityToken; // dto is the json that the apple sent to me, dto.signedPayload is a jws.
   var itor = jsonToken.Header["x5c"] as IReadOnlyList<object>;
   
   // certificate2.Thumbprint is same as AppleRootCA.Thumbprint
   X509Certificate2 certificate2 = new X509Certificate2(Convert.FromBase64String((string)itor[2]));
   X509Certificate2 certificate1 = new X509Certificate2(Convert.FromBase64String((string)itor[1]));
   X509Certificate2 certificate0 = new X509Certificate2(Convert.FromBase64String((string)itor[0]));
   
   // I have trusted the AppleRootCA-G3.cer before, so I don't need to call them again.
   // X509Store store = new X509Store(StoreName.Root, StoreLocation.CurrentUser);
   // store.Open(OpenFlags.ReadWrite);
   // store.Add(AppleRootCA);
   
   using var chain = new X509Chain();
   // chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
   // chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllowUnknownCertificateAuthority;
   chain.ChainPolicy.ExtraStore.Add(certificate2);
   chain.ChainPolicy.ExtraStore.Add(certificate1);
   chain.ChainPolicy.ExtraStore.Add(certificate0);
   var isValid = chain.Build(AppleRootCA);
   Console.WriteLine(isValid); // true
   

3. 令牌验证尝试：

   • 我尝试使用以下代码来验证令牌：

   var validationParameters = new TokenValidationParameters
   {
       ValidateIssuerSigningKey = true,
       IssuerSigningKey = new X509SecurityKey(AppleRootCA),
       ValidateIssuer = false,
       ValidateAudience = false,
       // RequireExpirationTime = true,
       ValidateLifetime = true,
       // TryAllIssuerSigningKeys = true
   };
   try
   {
       handler.ValidateToken(dto.signedPayload, validationParameters, out var st);
       // await handler.ValidateTokenAsync(jsonToken, validationParameters);
       Console.WriteLine("success");
       // return true;
   }
   catch (Exception ex)
   {
       Console.WriteLine($"false: {ex.Message}");
       // return false;
   }
   

   • 但是，我不断遇到以下错误：

   IDX10517: Signature validation failed. The token's kid is missing. Keys tried: 'Microsoft.IdentityModel.Tokens.X509SecurityKey, KeyId: 'B52CB02FD567E0359FE8FA4D4C41037970FE01B0', InternalId: 'tSywL9Vn4DWf6PpNTEEDeXD-AbA'. , KeyId: B52CB02FD567E0359FE8FA4D4C41037970FE01B0
   '. Number of keys in TokenValidationParameters: '1'.
   Number of keys in Configuration: '0'.
   Exceptions caught:
   '[PII of type 'System.Text.StringBuilder' is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'.
   token: '[PII of type 'System.IdentityModel.Tokens.Jwt.JwtSecurityToken' is hidden. For more details, see https://aka.ms/IdentityModel/PII.]'. See https://aka.ms/IDX10503 for details.
   

   • ChatGPT 建议我输入正确的

     IssuerSigningKey

     。我尝试将输入参数

     AppleRootCA

     更改为

     certificate0

     、

     certificate1

     和

     certificate2

     ，但同样的错误仍然存在。我目前很茫然，不知道如何确保这个JWS是有效的。我非常渴望获得一些帮助！

Answer 1

您可以先尝试从证书中获取公钥吗？

// Load the certificate
var certificate = new X509Certificate2(cerFilePath);
    
// Extract the public key
var securityKey = new RsaSecurityKey(certificate.GetRSAPublicKey());

 var tokenHandler = new JwtSecurityTokenHandler();
    var validationParameters = new TokenValidationParameters
    {
        // ValidateIssuer = true,
        // ValidIssuer = issuer,
        // ValidateAudience = true,
        // ValidAudience = audience,
        ValidateLifetime = true,
        IssuerSigningKey = securityKey,
        ValidateIssuerSigningKey = true
    };

    try
    {
       // token - you are getting at the time of callback
        var principal = tokenHandler.ValidateToken(token, validationParameters, out var validatedToken);
        return principal;
    }
    catch (SecurityTokenException)
    {
        // Token validation failed
        return null;
    }