C# 3.0 Cookbook, 3rd Edition

17.1. Controlling Access to Types in a Local Assembly

Problem

You have an existing class that contains sensitive data, and you do not want clients to have direct access to any objects of this class. Instead, you want an intermediary object to talk to the clients and to allow access to sensitive data based on the client's credentials. What's more, you would also like to have specific queries and modifications to the sensitive data tracked, so that if an attacker manages to access the object, you will have a log of what the attacker was attempting to do.

Solution

Use the proxy design pattern to allow clients to talk directly to a proxy object. This proxy object will act as gatekeeper to the class that contains the sensitive data. To keep malicious users from accessing the class itself, make it private, which will at least keep code without the ReflectionPermissionFlag. MemberAccess access (which is currently given only in fully trusted code scenarios such as executing code interactively on a local machine) from getting at it.

The namespaces we will be using are:

	using System;
	using System.IO;
	using System.Security;
	using System.Security.Permissions;
	using System.Security.Principal;

Let's start this design by creating an interface, as shown in Example 17-1, that will be common to both the proxy objects and the object that contains sensitive data.

Example 17-1. ICompanyData interface

internal interface ICompanyData { string AdminUserName { get; set; } string AdminPwd { get; set; } string CEOPhoneNumExt ...