public static ConfigurationManager UseAzureKeyVault(this ConfigurationManager manager, AzureKeyVaultSettingsProviderOptions options)
        {
            // RegisterSetting(AzureKeyVaultDefaults.DefaultAzureADClientSecretKey, converter: CryptoHelper.DecryptEnvelop);

            options.ConfigurationManager = manager;
            manager.AddSettingsProvider(new AzureKeyVaultSettingsProvider(options), options.LoadingOrder);
            return(manager);
        }
        public void TestMethod1()
        {
            //Add the following to your DI as a singleton.

            var config  = new ConfigurationManager(new AppSettingsProvider());
            var options = new AzureKeyVaultSettingsProviderOptions
            {
                ConfigurationManager = config,     //Used to get the clientid,secret and uri of vault.
                SecretConverter      = CryptoHelper.DecryptEnvelop
            };

            config.AddSettingsProvider(new AzureKeyVaultSettingsProvider(options));

            config.RegisterAzureKeyVaultSecret("sendgrid_secret");



            //In your application do IoC.Resolve<ConfigurationManager>();
            var secret = config.GetSetting <SecretBundle>("sendgrid_secret");
            var a      = config.GetAzureKeyVaultSecret("sendgrid_secret");

            //And there is your secret taht you can use.
        }