Differentiate between authentication and authorization. Explain the implementation of user authentication in a web application.

Authentication and authorization are two distinct concepts in the context of web applications.

Authentication refers to the process of verifying the identity of a user or entity. It ensures that the user is who they claim to be. This is typically done by requesting the user to provide credentials, such as a username and password. The system then compares these credentials with the stored ones to determine if they match. If the credentials are valid, the user is granted access to the system.

Authorization, on the other hand, is the process of granting or denying access to specific resources or functionalities within a system. Once a user has been authenticated, authorization determines what actions they are allowed to perform and what data they can access. This is typically based on the user's role or permissions assigned to them.

Now, let's discuss the implementation of user authentication in a web application. There are several common methods for implementing user authentication:

1. Username and password: This is the most common method where users provide a unique username and a password. The application then verifies these credentials against a database of stored usernames and hashed passwords.

2. Social media login: Many web applications allow users to authenticate using their social media accounts, such as Facebook or Google. In this case, the application relies on the authentication mechanisms provided by the social media platform.

3. Two-factor authentication (2FA): This adds an extra layer of security by requiring users to provide a second form of authentication, such as a temporary code sent to their mobile device, in addition to their username and password.

4. Single sign-on (SSO): SSO allows users to authenticate once and then access multiple applications or services without having to provide their credentials again. This is commonly used in enterprise environments.

To implement user authentication in a web application, the following steps are typically involved:

1. User registration: Users need to create an account by providing their details, such as username, password, and email address. This information is then stored securely in a database.

2. Login page: The application provides a login page where users can enter their credentials to authenticate themselves. The entered credentials are then validated against the stored information.

3. Session management: Once a user is authenticated, a session is created to maintain their authenticated state. This session is typically stored on the server and associated with the user's browser using a session ID.

4. Password security: It is crucial to store passwords securely by using techniques like hashing and salting. This ensures that even if the database is compromised, the passwords cannot be easily decrypted.

5. Error handling: Proper error handling should be implemented to provide meaningful error messages to users in case of authentication failures or other issues.

6. Logout functionality: Users should be provided with a way to log out of the application, which terminates their session and removes their access to protected resources.

By implementing these steps, a web application can effectively authenticate users and ensure that only authorized individuals can access the system's resources.