github-csharp-secrets-signature-validation.cs

// <PackageReference Include="Portable.BouncyCastle" Version="1.9.0" />

static void Main(string[] args)
{
    Console.WriteLine("Hello, World!");

    string payload = @"[{""token"":""some_token"",""type"":""some_type"",""url"":""some_url"",""source"":""some_source""}]";
    string signature = "MEUCIFLZzeK++IhS+y276SRk2Pe5LfDrfvTXu6iwKKcFGCrvAiEAhHN2kDOhy2I6eGkOFmxNkOJ+L2y8oQ9A2T9GGJo6WJY=";
    string pubKey = "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEsz9ugWDj5jK5ELBK42ynytbo38gPHzZFI03Exwz8Lh/tCfL3YxwMdLjB+bMznsanlhK0RwcGP3IDb34kQDIo3Q==\n-----END PUBLIC KEY-----\n";

    var encodedPayload = Encoding.UTF8.GetBytes(payload);
    var encodedSignature = Convert.FromBase64String(signature);

    using (var textReader = new StringReader(pubKey))
    {
        var parameter = (ECPublicKeyParameters)new PemReader(textReader).ReadObject();

        ISigner signer = SignerUtilities.GetSigner("SHA-256withECDSA");
        signer.Init(false, parameter);

        signer.BlockUpdate(encodedPayload, 0, encodedPayload.Length);
        Console.WriteLine(signer.VerifySignature(encodedSignature));
    }
}