Authenticate to keyvault using either certificate or secret

auth_kv.cs

public class CertificateHelper
{
    public static X509Certificate2 FindCertificateByThumbprint(string thumbrint)
    {
        X509Certificate2 cert;
        cert = FindCertificateByThumbprint(thumbrint, StoreName.My, StoreLocation.CurrentUser);
        if (cert == null)
        {
            cert = FindCertificateByThumbprint(thumbrint, StoreName.My, StoreLocation.LocalMachine);
        }
        return cert;
    }

    private static X509Certificate2 FindCertificateByThumbprint(string thumbrint, StoreName storeName, StoreLocation storeLocation)
    {
        using (X509Store store = new X509Store(storeName, storeLocation))
        {
            store.Open(OpenFlags.ReadOnly);
            X509Certificate2Collection certs = store.Certificates.Find(X509FindType.FindByThumbprint,
                thumbrint, false); // Don't validate certs, since the test root isn't installed.
            if (certs == null || certs.Count == 0)
                return null;
            return certs.OfType<X509Certificate2>().Single();
        }
    }
}

private static IKeyVaultClient CreateKeyVaultClientWithCertificate(string clientId, string certificateThumbrint)
{
    X509Certificate2 clientCertificate = CertificateHelper.FindCertificateByThumbprint(certificateThumbrint);
    if (clientCertificate == null)
    {
        throw new Exception($"Failed to find certificate with thumbprint {certificateThumbrint}");
    }
    var clientCredential = new ClientAssertionCertificate(clientId, clientCertificate);
    return CreateKeyVaultClient(async (AuthenticationContext authenticationContext, string resource) =>
    { return await authenticationContext.AcquireTokenAsync(resource, clientCredential); });
}

private static IKeyVaultClient CreateKeyVaultClientWithSecret(string clientId, string clientSecret)
{
    ClientCredential clientCredential = new ClientCredential(clientId, clientSecret);

    return CreateKeyVaultClient(async (AuthenticationContext authenticationContext, string resource) => 
        { return await authenticationContext.AcquireTokenAsync(resource, clientCredential); });
}

private static IKeyVaultClient CreateKeyVaultClient(TokenAcquireDelegateAsync tokenAcquireDelegateAsync)
{
    var tokenCache = new TokenCache();
    IKeyVaultClient keyVaultClient = new KeyVaultClient(async (authority, resource, scope) =>
    {
        AuthenticationContext authenticationContext = new AuthenticationContext(new Uri(authority).AbsoluteUri, false, tokenCache);
        AuthenticationResult result = await tokenAcquireDelegateAsync(authenticationContext, resource).ConfigureAwait(false);
        string token = result.AccessToken;
        return token;
    });
    return keyVaultClient;
}