private async Task <RSA> GetRSAProviderFromCertAsync(RequestSignature reqSignature)
{
_ = reqSignature ?? throw new ArgumentNullException(nameof(reqSignature));
_ = reqSignature.KeyId ?? throw new InvalidOperationException($"{nameof(reqSignature.KeyId)} is null");
var certUri = new Uri($"{_config.SmartThingsCertUriRoot}{reqSignature.KeyId}");
var certBytes = await _httpClient.GetByteArrayAsync(certUri).ConfigureAwait(false);
if (certBytes?.Length > 0)
{
using X509Certificate2 cert = new(certBytes);
return(cert.GetRSAPublicKey());
}
return(null);
}
public async Task <bool> VerifySignedRequestAsync(HttpRequest request)
{
_ = request ?? throw new ArgumentNullException(nameof(request));
_logger.LogDebug($"Verifying sign request: {request.Path}");
var reqSignature = RequestSignature.ParseFromHeaderVal(request.Headers["Authorization"].FirstOrDefault());
var hash = GetHash(reqSignature, request);
var data = Convert.FromBase64String(reqSignature.Signature);
var publicKeyProvider = await GetRSAProviderFromCertAsync(reqSignature).ConfigureAwait(false);
if (publicKeyProvider != null)
{
return(publicKeyProvider.VerifyData(hash, data, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1));
}
else
{
return(false);
}
}
private static byte[] GetHash(RequestSignature reqSignature, HttpRequest request)
{
var siginingString = new StringBuilder();
int headerCount = reqSignature.Headers.Count();
for (int i = 0; i < headerCount; i++)
{
var h = reqSignature.Headers.ElementAt(i);
if (h == "(request-target)")
{
siginingString.Append("(request-target): ");
siginingString.Append(request.Method.ToString(CultureInfo.InvariantCulture).ToLowerInvariant());
siginingString.Append(' ');
siginingString.Append(request.Path);
}
else
{
if (!request.Headers.TryGetValue(h, out StringValues vals))
{
throw new InvalidOperationException($"Missing {h} header per the auth header!");
}
siginingString.Append(h);
siginingString.Append(": ");
siginingString.Append(vals.FirstOrDefault());
}
if (i < (headerCount - 1))
{
siginingString.Append('\n');
}
}
var val = siginingString.ToString();
var encoding = UTF8Encoding.UTF8;
return(encoding.GetBytes(val));
}