Fix for heap access violation (#513)

Fixes a heap access violation found when implementing AppVerifier into the C++ V2 SDK CI. Now the code correctly only frees the pcerts manually when required.

source/windows/secure_channel_tls_handler.c

@@ -59,6 +59,7 @@ struct secure_channel_ctx {
     HCRYPTPROV crypto_provider;
     HCRYPTKEY private_key;
     bool verify_peer;
+    bool should_free_pcerts;
 };
 
 struct secure_channel_handler {
@@ -1841,7 +1842,15 @@ static void s_secure_channel_ctx_destroy(struct secure_channel_ctx *secure_chann
     }
 
     if (secure_channel_ctx->pcerts) {
-        CertFreeCertificateContext(secure_channel_ctx->pcerts);
+        /**
+         * Only free the private certificate context if the private key is NOT
+         * from the certificate context because freeing the private key
+         * using CryptDestroyKey frees the certificate context and then
+         * trying to access it leads to a access violation.
+         */
+        if (secure_channel_ctx->should_free_pcerts == true) {
+            CertFreeCertificateContext(secure_channel_ctx->pcerts);
+        }
     }
 
     if (secure_channel_ctx->cert_store) {
@@ -1887,6 +1896,7 @@ struct aws_tls_ctx *s_ctx_new(
 
     secure_channel_ctx->verify_peer = options->verify_peer;
     secure_channel_ctx->credentials.dwVersion = SCHANNEL_CRED_VERSION;
+    secure_channel_ctx->should_free_pcerts = true;
 
     secure_channel_ctx->credentials.grbitEnabledProtocols = 0;
 
@@ -2015,6 +2025,7 @@ struct aws_tls_ctx *s_ctx_new(
 
         secure_channel_ctx->credentials.paCred = &secure_channel_ctx->pcerts;
         secure_channel_ctx->credentials.cCreds = 1;
+        secure_channel_ctx->should_free_pcerts = false;
     }
 
     return &secure_channel_ctx->ctx;