public async Task <bool> IsValidRequest(HeaderObject headerObject, string body, string webHookId)
{
bool isValid = false;
try
{
HashAlgorithmName hashAlgorithm = ConvertAuthAlgorithmHeaderToHashAlgorithmName(headerObject.AuthenticationAlogrithm);
uint crc32 = Crc32.ComputeChecksum(body);
string expectedSignature = $"{headerObject.TransmissionId}|{headerObject.TransmissionTime}|{webHookId}|{crc32}";
byte[] expectedSignatureBytes = Encoding.UTF8.GetBytes(expectedSignature);
_logger.LogInformation($"Expected sig: {expectedSignature}");
_logger.LogInformation($"Cert url: {headerObject.CertificateUrl}");
var x509Certificate = await CertificateManager.Instance.GetCertificateFromUrl(headerObject.CertificateUrl);
using (var rsa = x509Certificate.GetRSAPublicKey())
{
byte[] signatureBytes = Convert.FromBase64String(headerObject.TransmissionSig);
//TODO: Implement Verification => || -> && with working verification of sigs
isValid = CertificateManager.Instance.ValidatePayPalClientCertificate(x509Certificate) ||
rsa.VerifyData(expectedSignatureBytes, signatureBytes, hashAlgorithm, RSASignaturePadding.Pss);
}
}
catch (Exception ex)
{
throw new Exception($"Encountered an error while attepting to validate a webhook event.", ex);
}
return(isValid);
}
protected async override Task <AuthenticateResult> HandleAuthenticateAsync()
{
HeaderObject headerObject = GetHeaderObject();
string body = await new StreamReader(Request.Body).ReadToEndAsync();
if (headerObject == null ||
!await _authenticationService.IsValidRequest(headerObject, await new StreamReader(Request.Body).ReadToEndAsync(), Options.WebHookId))
{
return(AuthenticateResult.Fail("Invalid transmission signature!"));
}
Request.Body.Position = 0;
IEnumerable <Claim> claims = new List <Claim>()
{
new Claim(ClaimTypes.Authentication, "true")
};
IEnumerable <ClaimsIdentity> identity = new List <ClaimsIdentity>()
{
new ClaimsIdentity(claims)
{
}
};
return(AuthenticateResult.Success(
new AuthenticationTicket(
new ClaimsPrincipal(identity),
new AuthenticationProperties
{
ExpiresUtc = DateTime.UtcNow.AddMinutes(15),
IsPersistent = false,
AllowRefresh = false
},
EventRequestAuthenticationDefaults.AuthenticationScheme)));
}
