Security Basics and ASP.NET Support
Introduction
What is the one thing forums, eCommerce sites, online email websites, portal websites, and social network sites all have in common? They all offer user accounts. Sites that offer user accounts must provide a number of services. At a minimum, new visitors need to be able to create an account and returning visitors must be able to log in. Such web applications can make decisions based on the logged in user: some pages or actions might be restricted to only logged in users, or to a certain subset of users; other pages might show information specific to the logged in user, or might show more or less information, depending on what user is viewing the page.This is the first tutorial in a series of tutorials that will explore techniques for authenticating visitors through a web form, authorizing access to particular pages and functionality, and managing user accounts in an ASP.NET application. Over the course of these tutorials we will examine how to:
- Identify and log users in to a website
- Use ASP.NET's Membership framework to manage user accounts
- Create, update, and delete user accounts
- Limit access to a web page, directory, or specific functionality based on the logged in user
- Use ASP.NET's Roles framework to associate user accounts with roles
- Manage user roles
- Limit access to a web page, directory, or specific functionality based on the logged in user's role
- Customize and extend ASP.NET's security Web controls
In this tutorial we will discuss important security concepts and what facilities are available in ASP.NET to assist in implementing forms authentication, authorization, user accounts, and roles. Let's get started!
Authentication, Authorization, User Accounts, and Roles
Authentication, authorization, user accounts, and roles are four terms that will be used very often throughout this tutorial series, so I'd like to take a quick moment to define these terms within the context of web security. In a client-server model, such as the Internet, there are many scenarios in which the server needs to identify the client making the request. Authentication is the process of ascertaining the client's identity. A client who has been successfully identified is said to be authenticated. An unidentified client is said to be unauthenticated or anonymous.Secure authentication systems involve at least one of the following three facets: something you know, something you have, or something you are. Most web applications rely on something the client knows, such as a password or a PIN. The information used to identify a user - her username and password, for example - are referred to as credentials. This tutorial series focuses on forms authentication, which is an authentication model where users log in to the site by providing their credentials in a web page form. We have all experienced this type of authentication before. Go to any eCommerce site. When you are ready to check out you are asked to log in by entering your username and password into textboxes on a web page.
In addition to identifying clients, a server may need to limit what resources or functionalities are accessible depending on the client making the request. Authorization is the process of determining whether a particular user has the authority to access a specific resource or functionality.
A user account is a store for persisting information about a particular user. User accounts must minimally include information that uniquely identifies the user, such as the user's login name and password. Along with this essential information, user accounts may include things like: the user's email address; the date and time the account was created; the date and time they last logged in; first and last name; phone number; and mailing address. When using forms authentication, user account information is typically stored in a relational database like Microsoft SQL Server.
Web applications that support user accounts may optionally group users into roles. A role is simply a label that is applied to a user and provides an abstraction for defining authorization rules and page-level functionality. For example, a website might include an Administrator role with authorization rules that prohibit anyone but an Administrator to access a particular set of web pages. Moreover, a variety of pages that are accessible to all users (including non-Administrators) might display additional data or offer extra functionality when visited by users in the Administrators role. Using roles, we can define these authorization rules on a role-by-role basis rather than user-by-user.
Authenticating Users in an ASP.NET Application
When a user enters a URL into their browser's address window or clicks on a link, the browser makes a Hypertext Transfer Protocol (HTTP) request to the web server for the specified content, be it an ASP.NET page, an image, a JavaScript file, or any other type of content. The web server is tasked with returning the requested content. In doing so, it must determine a number of things about the request, including who made the request and whether the identity is authorized to retrieve the requested content.By default, browsers send HTTP requests that lack any sort of identification information. But if the browser does include authentication information then the web server starts the authentication workflow, which attempts to identify the client making the request. The steps of the authentication workflow depend on the type of authentication being used by the web application. ASP.NET supports three types of authentication: Windows, Passport, and forms. This tutorial series focuses on forms authentication, but let's take a minute to compare and contrast Windows authentication user stores and workflow.
Authentication via Windows Authentication
The Windows authentication workflow uses one of the following authentication techniques:- Basic authentication
- Digest authentication
- Windows Integrated Authentication
Authentication via Forms Authentication
Forms authentication, on the other hand, is ideal for Internet web applications. Recall that forms authentication identifies the user by prompting them to enter their credentials through a web form. Consequently, when a user attempts to access an unauthorized resource, they are automatically redirected to the login page where they can enter their credentials. The submitted credentials are then validated against a custom user store - usually a database.After verifying the submitted credentials, a forms authentication ticket is created for the user. This ticket indicates that the user has been authenticated and includes identifying information, such as the username. The forms authentication ticket is (typically) stored as a cookie on the client computer. Therefore, subsequent visits to the website include the forms authentication ticket in the HTTP request, thereby enabling the web application to identify the user once they have logged in.
Figure 2 illustrates the forms authentication workflow from a high-level vantage point. Notice how the authentication and authorization pieces in ASP.NET act as two separate entities. The forms authentication system identifies the user (or reports that they are anonymous). The authorization system is what determines whether the user has access to the requested resource. If the user is unauthorized (as they are in Figure 2 when attempting to anonymously visit ProtectedPage.aspx), the authorization system reports that the user is denied, causing the forms authentication system to automatically redirect the user to the login page.
Once the user has successfully logged in, subsequent HTTP requests include the forms authentication ticket. The forms authentication system merely identifies the user - it is the authorization system that determines whether the user can access the requested resource.
Limiting Access to Web Pages, Directories, and Page Functionality
ASP.NET includes two ways to determine whether a particular user has authority to access a specific file or directory:- File authorization - since ASP.NET pages and web services are implemented as files that reside on the web server's file system, access to these files can be specified through Access Control Lists (ACLs). File authorization is most commonly used with Windows authentication because ACLs are permissions that apply to Windows accounts. When using forms authentication, all operating system- and file system-level requests are executed by the same Windows account, regardless of the user visiting the site.
- URL authorization - with URL authorization, the page developer specifies authorization rules in Web.config. These authorization rules specify what users or roles are allowed to access or are denied from accessing certain pages or directories in the application.
User Accounts and Roles
ASP.NET's forms authentication provides an infrastructure for users to log in to a site and have their authenticated state remembered across page visits. And URL authorization offers a framework for limiting access to specific files or folders in an ASP.NET application. Neither feature, however, supplies a means for storing user account information or managing roles.Today, implementing user accounts in an ASP.NET application is much simpler thanks to the Membership framework and the built-in Login Web controls. The Membership framework is a handful of classes in the System.Web.Security namespace that provide functionality for performing essential user account-related tasks. The key class in the Membership framework is the Membership class, which has methods like:
- CreateUser
- DeleteUser
- GetAllUsers
- GetUser
- UpdateUser
- ValidateUser
Microsoft ships two Membership provider classes in the .NET Framework:
- ActiveDirectoryMembershipProvider - implements the Membership API in Active Directory and Active Directory Application Mode (ADAM) servers.
- SqlMembershipProvider - implements the Membership API in a SQL Server database.
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