Azure keyvault prefix manager and usage

PrefixKeyVaultSecretManager.cs

using Microsoft.Azure.KeyVault.Models;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Configuration.AzureKeyVault;

namespace Demo.Azure.KeyVault
{
    public class PrefixKeyVaultSecretManager : IKeyVaultSecretManager
    {
        private readonly string _prefix;

        public PrefixKeyVaultSecretManager(string prefix)
        {
            _prefix = $"{prefix}-".ToLowerInvariant();
        }

        public bool Load(SecretItem secret)
        {
            return secret.Identifier.Name.StartsWith(_prefix);
        }

        public string GetKey(SecretBundle secret)
        {
            return secret.SecretIdentifier.Name
                .Substring(_prefix.Length)
                .Replace("--", ConfigurationPath.KeyDelimiter);
        }
    }
}

Startup.cs

public static class ServiceExtensions
{
    /// <summary>
    /// Creates a custom configuration for easier development of Azure Functions.
    /// When environment is not Development, it adds a keyvault provider
    /// </summary>
    /// <param name="builder"></param>
    /// <returns></returns>
    public static IConfiguration GetCustomConfiguration(this IFunctionsHostBuilder builder)
    {
        IConfiguration localConfiguration;

        if (Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Development")
        {
            localConfiguration = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables()
                .Build() as IConfiguration;
        }
        else
        {
            var rootConfig = builder.Services.BuildServiceProvider().GetRequiredService<IConfiguration>();
            var keyVaultBaseUrl = rootConfig.GetValue<string>("KeyVaultBaseUrl");

            // add keyvault
            localConfiguration = new ConfigurationBuilder()
                .AddAzureKeyVault(keyVaultBaseUrl, new PrefixKeyVaultSecretManager("prefix"))
                .AddEnvironmentVariables()
                .Build() as IConfiguration;

            // we have to replace the rootConfig with the new one that has keyVault
            builder.Services.AddSingleton(localConfiguration);
        }

        return localConfiguration;
    }
}