Improving Web Application Security: Threats and - CGISecurity

Chapter 10: Building Secure ASP.NET Pages and Controls 285Use Explicit Role Checks for Fine-Grained AuthorizationDeclarative security checks prevent a user from accessing a class or calling a specificmethod. If you need additional logic inside a method to make authorizationdecisions, either use imperative principal permission demands or explicit role checksusing IPrincipal.IsInRole. These approaches allow you to use additional runtimevariables to fine tune the authorization decision. The following example shows theuse of an imperative principal permission demand:// Imperative syntaxpublic void SomeRestrictedMethod(){// Only callers that are members of the specified Windows group// are allowed accessPrincipalPermission permCheck = new PrincipalPermission(null, @"DomainName\WindowsGroup");permCheck.Demand();// Some restricted operations (omitted)}The following example shows the use of IPrincipal.IsInRole:public void TransferMoney( string fromAccount,string toAccount, double amount){// Extract the authenticated user from the current HTTP context.// The User variable is equivalent to HttpContext.Current.User if you// are using an .aspx page (or .asmx)WindowsPrincipal authenticatedUser = User as WindowsPrincipal;if (null != authenticatedUser){// Note: To retrieve the authenticated user's username, use the// following line of code// string username = authenticatedUser.Identity.Name;// If the amount exceeds a threshold value, manager approval is requiredif (amount > thresholdValue) {// Perform a role checkif (authenticatedUser.IsInRole(@"DomainName\Manager") ){// OK to proceed with transfer}else{throw new Exception("Unauthorized funds transfer");}}else{. . .}}}