ae.net.ssl.schannel: Clean up failed credential setup

Allow the identity-import validation probe to acquire accessible CNG-backed
certificate keys with CRYPT_ACQUIRE_ALLOW_NCRYPT_KEY_FLAG. This is an
acquisition flag only; server PFX imports retain their machine-keyset scope
without adding a CNG-preference import flag.

When key validation fails after selecting an imported certificate with a
private key, delete its provider-specific persisted container before freeing
the certificate context. This preserves the existing persist-then-delete
lifecycle even when setup fails before ownership transfers to certContext.

Synchronous adapter initialization now releases acquired SSPI credential and
context handles if it throws while still allowing the exception to escape
createAdapter. Release SChannel output buffers with scope-exit cleanup so an
exception from next.send cannot leak a handshake or close-notify buffer.

The Linux ae_unittest suite passed. The full Windows SChannel suite passed
through a key-authenticated SSH logon, including the PFX echo and curl tests.
A disposable forced-CNG run also asserted CERT_NCRYPT_KEY_SPEC and passed
all SChannel tests.

Author: codex

net/ssl/schannel.d

@@ -143,6 +143,7 @@ extern(Windows) nothrow @nogc
 // (set by PFXImportCertStore without PKCS12_NO_PERSIST_KEY, readable by LSASS).
 enum DWORD CERT_KEY_PROV_INFO_PROP_ID = 2;
 enum DWORD CERT_NCRYPT_KEY_SPEC = 0xFFFFFFFF;
+enum DWORD CRYPT_ACQUIRE_ALLOW_NCRYPT_KEY_FLAG = 0x00010000;
 
 // Key provider info structure returned by CertGetCertificateContextProperty for
 // CERT_KEY_PROV_INFO_PROP_ID.  dwProvType == 0 ⇒ CNG key; != 0 ⇒ legacy CSP.
@@ -330,13 +331,19 @@ class SChannelContext : SSLContext
 
         if (!chosen)
             throw new Exception("setIdentityFromPKCS12: PFX contains no certificates");
-        scope(failure) CertFreeCertificateContext(chosen);
+        scope(failure)
+        {
+            if (chosenHasKey)
+                deleteKeyContainerSilent(chosen);
+            CertFreeCertificateContext(chosen);
+        }
 
         ULONG_PTR hKey;
         DWORD keySpec;
         BOOL callerFree;
         sspiEnforce(CryptAcquireCertificatePrivateKey(
-            chosen, 0, null, &hKey, &keySpec, &callerFree) != 0,
+            chosen, CRYPT_ACQUIRE_ALLOW_NCRYPT_KEY_FLAG, null,
+            &hKey, &keySpec, &callerFree) != 0,
             "CryptAcquireCertificatePrivateKey", cast(SECURITY_STATUS) GetLastError());
         if (callerFree)
         {
@@ -538,7 +545,10 @@ class SChannelAdapter : SSLAdapter
         this.context = context;
         super(next);
         if (next.state == ConnectionState.connected)
+        {
+            scope(failure) cleanupContext();
             initialize();
+        }
     }
 
     override void onConnect()
@@ -1062,11 +1072,11 @@ protected:
                 serverReqFlags(), 0, &hCtxt, &outDesc, &attr, &ts);
         }
 
+        scope(exit)
+            if (outBuf.pvBuffer)
+                FreeContextBuffer(outBuf.pvBuffer);
         if (outBuf.cbBuffer && outBuf.pvBuffer)
-        {
             next.send(Data((cast(ubyte*) outBuf.pvBuffer)[0 .. outBuf.cbBuffer]));
-            FreeContextBuffer(outBuf.pvBuffer);
-        }
     }
 
     private void cleanupContext()
@@ -1095,16 +1105,17 @@ protected:
 
     private void sendAndFreeOutputBuffers(SecBuffer[] bufs)
     {
+        scope(exit)
+            foreach (ref b; bufs)
+                if (b.pvBuffer)
+                {
+                    FreeContextBuffer(b.pvBuffer);
+                    b.pvBuffer = null;
+                    b.cbBuffer = 0;
+                }
         foreach (ref b; bufs)
-        {
             if (b.cbBuffer && b.pvBuffer)
-            {
                 next.send(Data((cast(ubyte*) b.pvBuffer)[0 .. b.cbBuffer]));
-                FreeContextBuffer(b.pvBuffer);
-                b.pvBuffer = null;
-                b.cbBuffer = 0;
-            }
-        }
     }
 }