Simple wrapper around .NET appSettings.

App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
    <appSettings>
      <add key="environment-type" value="Local" />
      <!--<add key="environment-log-minimum-level" value="Debug" />-->
      <add key="auth0-client-id" value="abc123abc" />
      <add key="auth0-client-secret" value="123abc123abc" />
      <add key="auth0-domain" value="abc123.auth0.com" />
      <add key="auth0-database-connection-name" value="ABC123" />
      <add key="auth0-token-expiration-seconds" value="3600" />
    </appSettings>
</configuration>

program.cs

using System;
using System.Configuration;
using System.Diagnostics;
using System.Text.RegularExpressions;
using Castle.Components.DictionaryAdapter;
using Serilog.Events;

namespace StronglyTypedAppSettings
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            var factory = new DictionaryAdapterFactory();

            var environment = factory.GetAdapter<IEnvironment>(ConfigurationManager.AppSettings);
            var auth0 = factory.GetAdapter<IAuth0>(ConfigurationManager.AppSettings);

            Debug.Assert(environment.Type == EnvironmentType.Local);
            Debug.Assert(auth0.TokenExpirationSeconds == 3600);
        }
    }

    [AppSettingWrapper]
    public interface IEnvironment
    {
        EnvironmentType Type { get; }

        LogEventLevel LogMinimumLevel { get; }
    }

    [AppSettingWrapper]
    public interface IAuth0
    {
        string ClientId { get; }
        string ClientSecret { get; }
        string Domain { get; }
        string DatabaseConnectionName { get; }
        int TokenExpirationSeconds { get; }
    }

    public enum EnvironmentType
    {
        Undefined,
        Local,
        Test,
        Uat,
        Production
    }

    public class AppSettingWrapperAttribute : DictionaryBehaviorAttribute, IDictionaryKeyBuilder,
        IPropertyDescriptorInitializer, IDictionaryPropertyGetter
    {
        private readonly Regex converter = new Regex("([A-Z])", RegexOptions.Compiled);

        public string GetKey(IDictionaryAdapter dictionaryAdapter, string key, PropertyDescriptor property)
        {
            var name = dictionaryAdapter.Meta.Type.Name.Remove(0, 1) + key;
            var adjustedKey = converter.Replace(name, "-$1").Trim('-');
            return adjustedKey;
        }

        public object GetPropertyValue(IDictionaryAdapter dictionaryAdapter, string key, object storedValue,
            PropertyDescriptor property, bool ifExists)
        {
            if (storedValue != null) return storedValue;
            throw new InvalidOperationException(string.Format("App setting '{0}' not found!", key.ToLowerInvariant()));
        }

        public void Initialize(PropertyDescriptor propertyDescriptor, object[] behaviors)
        {
            propertyDescriptor.Fetch = true;
        }
    }
}