Implement RSACertificateExtensions.CopyWithPrivateKey(). #14152. (#14860)

* Implement RSACertificateExtensions.CopyWithPrivateKey().  #14152.

* RSACertificateExtensions.CopyWithPrivateKey(): implement.

Since `RSACertificateExtensions` lives in `System.Core` and only `mscorlib`
internals (but not `System` internals) are visible to it, we need to use a
little trick here:

* System.Security.Cryptography.X509Certificates.X509CertificateImpl:
  add new abstract methods CopyWithPrivateKey() and CreateCertificate().

* System.Security.Cryptography.X509Certificates.X509Certificate2Impl:
  sealed implement them here.

The `httpcfg` tool, only checks whether the key is valid, so we don't really
need to call `CopyWithPrivateKey()` (which requires us to take a dependency
on `System.Core`).

* Do the same thing in HttpListener.

2 files changed, 14 insertions, 2 deletions

diff --git a/mcs/class/System/System.Net/HttpListener.Mono.cs b/mcs/class/System/System.Net/HttpListener.Mono.cs
index 5e673b9d5f0..c95c725ade9 100644
--- a/mcs/class/System/System.Net/HttpListener.Mono.cs
+++ b/mcs/class/System/System.Net/HttpListener.Mono.cs
@@ -80,8 +80,8 @@ namespace System.Net {
 					if (!File.Exists (pvk_file))
 						return null;
 					var cert = new X509Certificate2 (cert_file);
-					cert.PrivateKey = PrivateKey.CreateFromFile (pvk_file).RSA;
-					certificate = cert;
+					var privateKey = PrivateKey.CreateFromFile (pvk_file).RSA;
+					certificate = new X509Certificate2 ((X509Certificate2Impl)cert.Impl.CopyWithPrivateKey (privateKey));
 					return certificate;
 				} catch {
 					// ignore errors
diff --git a/mcs/class/System/System.Security.Cryptography.X509Certificates/X509Certificate2Impl.cs b/mcs/class/System/System.Security.Cryptography.X509Certificates/X509Certificate2Impl.cs
index a454ea07ada..6c6ad684a34 100644
--- a/mcs/class/System/System.Security.Cryptography.X509Certificates/X509Certificate2Impl.cs
+++ b/mcs/class/System/System.Security.Cryptography.X509Certificates/X509Certificate2Impl.cs
@@ -83,6 +83,18 @@ namespace System.Security.Cryptography.X509Certificates
 
 		public abstract void AppendPrivateKeyInfo (StringBuilder sb);
 
+		public sealed override X509CertificateImpl CopyWithPrivateKey (RSA privateKey)
+		{
+			var impl = (X509Certificate2Impl)Clone ();
+			impl.PrivateKey = privateKey;
+			return impl;
+		}
+
+		public sealed override X509Certificate CreateCertificate ()
+		{
+			return new X509Certificate2 (this);
+		}
+
 		public abstract void Reset ();
 	}
 }