Prevent false use of loading the application certificate, causing 'Keyset not valid' error. (Windows)

[mregen]

Type of Issue
[X] Bug [X] Enhancement [ ] Compliance [ ] Question [ ] Help wanted

Applies only for App certificate in Directory store on Windows:

When the app cert is not loaded through the xml appconfiguration API,
calling

ApplicationConfiguration.SecurityConfiguration.ApplicationCertificate.Find(true);

before

ApplicationConfiguration.SecurityConfiguration.ApplicationCertificate.LoadPrivateKey(null)

causes the certificate to be loaded without proper keyset for encrypt/decrypt.
A call to GetRSAPrivateKey throws exception. Encryption and signing will not work.

To Reproduce

in your code, load Findor Update before LoadPrivateKey, causes the cert to have invalid KeySet.
A call to GetRSAPrivateKey throws exception. Encrypion and signing will not work.

Expected behavior

API is able to load private key even if calls are not in the right order.

Code snippets

At this time, known working pseudo code:

            // reload the application certificate with private key, if it is there
            // note: do not change this sequence, or the private key is not properly loaded on some platforms
            if (await applicationConfiguration.SecurityConfiguration.ApplicationCertificate.LoadPrivateKey(null).ConfigureAwait(false) != null)
            {
                // update certificate with private key
                certificate = await ApplicationConfiguration.SecurityConfiguration.ApplicationCertificate.Find(true).ConfigureAwait(false);
            }

            // create a self signed certificate if there is none
            if (certificate == null)
            {
                certificate = CertificateFactory.CreateCertificate(
                    applicationConfiguration.SecurityConfiguration.ApplicationCertificate.StoreType,
                    applicationConfiguration.SecurityConfiguration.ApplicationCertificate.StorePath,
                    null,
                    applicationConfiguration.ApplicationUri,
                    applicationConfiguration.ApplicationName,
                    applicationConfiguration.ApplicationName,
                    null,
                    CertificateFactory.DefaultKeySize,
                    DateTime.UtcNow - TimeSpan.FromDays(1),
                    CertificateFactory.DefaultLifeTime,
                    CertificateFactory.DefaultHashSize,
                    false,
                    null,
                    null
                    );
                // reload the certificate from disk.
                certificate = await applicationConfiguration.SecurityConfiguration.ApplicationCertificate.LoadPrivateKey(null);
                if (certificate == null)
                {
                    throw new Exception("OPC UA application certificate can not be loaded from disk!");
                }
                else
                {
                    // update certificate with private key
                    certificate = await applicationConfiguration.SecurityConfiguration.ApplicationCertificate.Find(true).ConfigureAwait(false);
                }
            }
  
            // update security information
            await applicationConfiguration.CertificateValidator.Update(applicationConfiguration.SecurityConfiguration).ConfigureAwait(false);

Environment (please complete the following information):

• OS: Windows
• Development environment: any VS
• Runtime: all .NET 4.6.2, .NET Core x.1
• OPC Package Release Version 1.4.363.107
• Component: Opc.Ua.Core

[mregen]

fixed in #1209

[mregen]

still repro in 366 release...