Added RSAKeyVaultWrapper that resolves calls to the ExportParameters method of the RSAKeyVault.

src/Sign.SignatureProviders.KeyVault/KeyVaultService.cs

@@ -83,7 +83,10 @@ public async Task<X509Certificate2> GetCertificateAsync(CancellationToken cancel
 
         public async Task<RSA> GetRsaAsync(CancellationToken cancellationToken)
         {
-            return await _cryptographyClient.CreateRSAAsync(cancellationToken);
+            using X509Certificate2 certificate = await GetCertificateAsync(cancellationToken);
+            RSAKeyVault rsaKeyVault = await _cryptographyClient.CreateRSAAsync(cancellationToken);
+            RSA rsaPublicKey = certificate.GetRSAPrivateKey()!;
+            return new RSAKeyVaultWrapper(rsaKeyVault, rsaPublicKey);
         }
     }
 }

src/Sign.SignatureProviders.KeyVault/RSAKeyVaultWrapper.cs

@@ -0,0 +1,52 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE.txt file in the project root for more information.
+
+using System.Security.Cryptography;
+using Azure.Security.KeyVault.Keys.Cryptography;
+
+namespace Sign.SignatureProviders.KeyVault
+{
+    internal sealed class RSAKeyVaultWrapper : RSA
+    {
+        private readonly RSAKeyVault _rsaKeyVault;
+        private readonly RSA _rsaPublicKey;
+
+        public RSAKeyVaultWrapper(RSAKeyVault rsaKeyVault, RSA publicKey)
+        {
+            _rsaKeyVault = rsaKeyVault;
+            _rsaPublicKey = publicKey;
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _rsaKeyVault.Dispose();
+                _rsaPublicKey.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+
+
+        public override RSAParameters ExportParameters(bool includePrivateParameters)
+        {
+            if (includePrivateParameters)
+            {
+                throw new NotSupportedException();
+            }
+
+            return _rsaPublicKey.ExportParameters(false);
+        }
+
+        public override void ImportParameters(RSAParameters parameters)
+            => throw new NotImplementedException();
+
+        public override byte[] SignHash(byte[] hash, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding)
+            => _rsaKeyVault.SignHash(hash, hashAlgorithm, padding);
+
+        public override bool VerifyHash(byte[] hash, byte[] signature, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding)
+            => _rsaPublicKey.VerifyHash(hash, signature, hashAlgorithm, padding);
+    }
+}