protected override void Initialize(RequestContext requestContext)
        {
            if (requestContext.HttpContext.User.Identity is WindowsIdentity)
            {
                throw new InvalidOperationException("Windows authentication is not supported.");
            }
            else
            {
                base.Initialize(requestContext);
            }

        public const string SafeUrlCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.~";

        /// <summary>
        /// Encrypts a string at the current user's scope using DPAPI.
        /// </summary>
        /// <param name="toEncrypt">The string to encrypt.</param>
        /// <param name="key">The key used to encrypt it.</param>
        /// <returns>
        /// The encrypted bytes that only the current user, with the specified key,
        /// can decrypt again.
        /// </returns>
        /// <seealso cref="CR_CodeTweet.ByteExtensions.Decrypt" />

        /// <summary>
        /// URL-encodes a string for use with OAuth.
        /// </summary>
        /// <param name="toEncode">
        /// The string to encode.
        /// </param>
        /// <returns>
        /// A URL-encoded string where all of the encoded characters are upper-case.
        /// </returns>
        /// <remarks>

    public abstract class ContentPreprocessorBase
    {
        abstract protected string PreprocessContent(string stringToProcess);