MustBeAuthorizedAttribute.cs

public class MustBeAuthorizedAttribute : AuthorizationFilterAttribute
{
    public override void OnAuthorization(HttpActionContext actionContext)
    {
        if (Thread.CurrentPrincipal.Identity.IsAuthenticated)
        {
            return;
        }

        var authHeader = actionContext.Request.Headers.Authorization;

        if (authHeader != null)
        {
            if (authHeader.Scheme == "Basic" && !string.IsNullOrEmpty(authHeader.Parameter))
            {
                try
                {
                    var credentials = ExtractCredentials(authHeader.Parameter);
                    var username = credentials[0];
                    var password = credentials[1];

                    if (username == "administrator" && password == "password")
                    {
                        var currentPrincipal = new GenericPrincipal(new GenericIdentity(username), null);
                        Thread.CurrentPrincipal = currentPrincipal;
                    }
                }
                catch
                {
                    actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.Unauthorized);
                }
            }
        }
        else
        {
            actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.Unauthorized);
        }
    }


    private static string[] ExtractCredentials(string authParam)
    {
        var credentials = Encoding.Default.GetString(Convert.FromBase64String(authParam));
        return credentials.Split(':');
    }
}