namespace AdvantageCSP.WebAPI
{
    public class SecureContentControllerHandler : AdvantageSecureContentControllerHandler
    {
        private static string myKey = "d32b2c8c-dc57-4978-bf98-7c82db7c027c";

        private class AuthResponse
        {
            public string UserName { get; set; }
            public string Password { get; set; }
            public DateTime TimeStamp { get; set; }
        }

        public override AdvantageAuthResponse AuthenticateRequest(HttpRequestMessage request)
        {
            var credentials = ParseAuthorizationHeader(request);
            if (credentials != null)
                return new AdvantageAuthResponse() { Success = true };
            else
                return new AdvantageAuthResponse() { Success = false };
        }

        private AuthResponse ParseAuthorizationHeader(HttpRequestMessage request)
        {
            try
            {
                AuthResponse result = new AuthResponse();
                string authHeader = null;
                var auth = request.Headers.Authorization;
                if (auth != null && auth.Scheme == "Basic") authHeader = auth.Parameter;
                if (string.IsNullOrEmpty(authHeader)) return null;

                authHeader = Encryption.Decrypt(Encoding.Default.GetString(Convert.FromBase64String(authHeader)), myKey);
                var tokens = authHeader.Split(':');
                if (tokens.Length < 3) return null;
                result.UserName = tokens[0];
                result.Password = tokens[1];
                result.TimeStamp = DateTimeOffset.FromUnixTimeSeconds(Convert.ToInt64(tokens[2])).DateTime;

                return result;
            }
            catch
            {
                return null;
            }
        }

        // Sample of some authorization header for use in secure api.
        public static string GenerateAuthHeader()
        {
            string username = "SomeName";
            string password = "SomePassword";
            string datetime = DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString();
            byte[] data = Encoding.ASCII.GetBytes(Encryption.Encrypt($"{username}:{password}:{datetime}", myKey));
            return "{"Authorization": "Basic " + Convert.ToBase64String(data).ToString() + ""}";
        }
    }
}

Global.asax Configuration

<script runat="server">
    void Application_Start(object sender, EventArgs e)
    {
        AdvantageCSP.API.WebApiConfig.Register(GlobalConfiguration.Configuration, new AdvantageCSP.WebAPI.SecureContentControllerHandler());
    }
</script>