使用ITFoxTec SAML2与Azure KeyVault时解密密钥遇403禁止错误

背景 #

我们基于.NET 6 MVC框架，使用ITfoxtec Identity SAML 2.0包实现了与丹麦KOMBIT系统（外部身份提供商）的SSO集成，参考官方示例将Azure KeyVault用于加密操作。

更新证书后，新证书的密钥用途仅包含KeyEncipherment标识，不再具备DataEncipherment标识。此时接收并解密来自身份提供商的SAML响应时，Azure KeyVault返回403禁止响应，证书根CA为Den Danske Stat OCES rod-CA。

相关SAML2Configuration配置 #

var saml2Configuration = new Saml2Configuration
{
    Issuer = _config.Issuer,
    SignatureAlgorithm = _config.SignatureAlgorithm,
    CertificateValidationMode = _config.CertificateValidationMode,
    RevocationMode = _config.RevocationMode
};

var certificateClient = new CertificateClient(new Uri(AzureKeyVaultBaseUrl), _tokenCredential);
var certificateWithPolicy = certificateClient.GetCertificate(AzureKeyVaultCertificateName);

var publicCertificate = new X509Certificate2(certificateWithPolicy.Value.Cer);
var rsa = RSAFactory.Create(_tokenCredential, certificateWithPolicy.Value.KeyId, 
    new Azure.Security.KeyVault.Keys.JsonWebKey(publicCertificate.GetRSAPublicKey()));

saml2Configuration.SigningCertificate = new Saml2X509Certificate(publicCertificate, rsa);
saml2Configuration.DecryptionCertificates = new List<X509Certificate2>()
    {new Saml2X509Certificate(publicCertificate, rsa)};

saml2Configuration.SignAuthnRequest = true;

回调端点读取SAML响应代码 #

var binding = new Saml2PostBinding();
var saml2AuthResponse = new Saml2AuthnResponse(_saml2Configuration);
var httpRequest = Request.ToGenericHttpRequest();

binding.ReadSamlResponse(httpRequest, saml2AuthResponse);

抛出异常信息 #

System.Security.Cryptography.CryptographicException: Error calling Key Vault
 ---> Azure.RequestFailedException: Operation decrypt is not permitted on this key.
Status: 403 (Forbidden)
ErrorCode: Forbidden

Content:
{"error":{"code":"Forbidden","message":"Operation decrypt is not permitted on this key.","innererror":{"code":"KeyOperationForbidden"}}}

   at Azure.Security.KeyVault.KeyVaultPipeline.SendRequest(Request request, CancellationToken cancellationToken)
   at Azure.Security.KeyVault.KeyVaultPipeline.SendRequest[TContent,TResult](RequestMethod method, TContent content, Func`1 resultFactory, CancellationToken cancellationToken, String[] path)
   at Azure.Security.KeyVault.Keys.Cryptography.RemoteCryptographyClient.Decrypt(DecryptParameters parameters, CancellationToken cancellationToken)
   at Azure.Security.KeyVault.Keys.Cryptography.CryptographyClient.Decrypt(DecryptParameters decryptParameters, CancellationToken cancellationToken)
   at Azure.Security.KeyVault.Keys.Cryptography.CryptographyClient.Decrypt(EncryptionAlgorithm algorithm, Byte[] ciphertext, CancellationToken cancellationToken)
   at RSAKeyVaultProvider.KeyVaultContext.DecryptData(Byte[] cipherText, RSAEncryptionPadding padding) in /_/RSAKeyVaultProvider/KeyVaultContext.cs:line 104
   at RSAKeyVaultProvider.RSAKeyVault.Decrypt(Byte[] data, RSAEncryptionPadding padding) in /_/RSAKeyVaultProvider/RSAKeyVault.cs:line 87
   --- End of inner exception stack trace ---
   at RSAKeyVaultProvider.RSAKeyVault.Decrypt(Byte[] data, RSAEncryptionPadding padding) in /_/RSAKeyVaultProvider/RSAKeyVault.cs:line 91
   at System.Security.Cryptography.RSAOAEPKeyExchangeDeformatter.DecryptKeyExchange(Byte[] rgbData)
   at System.Security.Cryptography.Xml.EncryptedXml.DecryptKey(Byte[] keyData, RSA rsa, Boolean useOAEP)
   at ITfoxtec.Identity.Saml2.Cryptography.Saml2EncryptedXml.DecryptEncryptedKey(EncryptedKey encryptedKey)
   at System.Security.Cryptography.Xml.EncryptedXml.GetDecryptionKey(EncryptedData encryptedData, String symmetricAlgorithmUri)
   at System.Security.Cryptography.Xml.EncryptedXml.DecryptDocument()
   at ITfoxtec.Identity.Saml2.Saml2AuthnResponse.DecryptMessage()
   at ITfoxtec.Identity.Saml2.Saml2Request.Read(String xml, Boolean validateXmlSignature, Boolean detectReplayedTokens)
   at ITfoxtec.Identity.Saml2.Saml2Response.Read(String xml, Boolean validateXmlSignature, Boolean detectReplayedTokens)
   at ITfoxtec.Identity.Saml2.Saml2AuthnResponse.Read(String xml, Boolean validateXmlSignature, Boolean detectReplayedTokens)
   at ITfoxtec.Identity.Saml2.Saml2PostBinding.Read(HttpRequest request, Saml2Request saml2RequestResponse, String messageName, Boolean validateXmlSignature, Boolean detectReplayedTokens)
   at ITfoxtec.Identity.Saml2.Saml2Binding`1.ReadSamlResponse(HttpRequest request, Saml2Response saml2Response)
   at "our code"

已尝试方案 #

• 调试确认ITfoxtec.Identity.Saml2.Cryptography.Saml2EncryptedXml.DecryptEncryptedKey最终调用RSAKeyVaultProvider.KeyVaultContext.DecryptData，该方法向Azure KeyVault发起的API请求返回禁止响应
• 临时修改第三方库中该方法的API调用为UnwrapKey后功能恢复正常，但不希望修改第三方库实现

疑问 #

原本期望通过接受RSA参数的Saml2X509Certificate构造函数继续集成，但System.Security.Cryptography的RSA类没有DecryptKey方法，仅包含Decrypt方法。使用无DataEncipherment标识的证书，是否无法再遵循示例完成集成？

内容的提问来源于stack exchange，提问作者madsatwork