Example of a Custom Configuration Section. Can be used in conjunction with Config Transforms to provide different custom configuration per build/environment.

BobsBurgersConfiguration.cs

using System;
using System.Configuration;

namespace Example.Configuration
{
    internal class BobsBurgersConfiguration : ConfigurationSection
    {
        /// <summary>
        /// The BobsBurgers ConfigurationSection name.
        /// </summary>
        private readonly static string _bobsBurgersConfiguration = "bobsBurgersConfiguration";

        /// <summary>
        /// The settings for the BobsBurgers ConfigurationSection.
        /// </summary>
        private static BobsBurgersConfiguration _settings = System.Configuration.ConfigurationManager.GetSection(_bobsBurgersConfiguration) as BobsBurgersConfiguration;

        /// <summary>
        /// Gets the settings.
        /// </summary>
        /// <value>
        /// The settings.
        /// </value>
        public static BobsBurgersConfiguration Settings
        {
            get
            {
                return _settings;
            }
        }

        /// <summary>
        /// Gets the environment.
        /// </summary>
        /// <value>
        /// The environment.
        /// </value>
        [ConfigurationProperty("environment", IsRequired = true)]
        public string Environment
        {
            get
            {
                return (string)this["environment"];
            }
        }

        /// <summary>
        /// Gets the public key.
        /// </summary>
        /// <value>
        /// The public key.
        /// </value>
        [ConfigurationProperty("publicKey", IsRequired = true)]
        public string PublicKey
        {
            get
            {
                return (string)this["publicKey"];
            }
        }

        /// <summary>
        /// Gets the private key.
        /// </summary>
        /// <value>
        /// The private key.
        /// </value>
        [ConfigurationProperty("privateKey", IsRequired = true)]
        public string PrivateKey
        {
            get
            {
                return (string)this["privateKey"];
            }
        }
    }
}

Web.config

<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=301880
  -->
<configuration>
  <configSections>
    <section name="bobsBurgersConfiguration" type="Example.Configuration.BobsBurgersConfiguration" allowLocation="true" allowDefinition="Everywhere"></section>
  </configSections>
  <bobsBurgersConfiguration environment="DEV" publicKey="PUBLICKEY" privateKey="PRIVATEKEY" />
</configuration>