Before delving into the implementation, it's important to distinguish between two key concepts: authentication and authorization. Authentication is the process of verifying a user's identity, typically through a username and password. Authorization, on the other hand, determines what resources and operations an authenticated user can access.

Step 1: Setting Up the Database

The foundation is preparing the database for storing user data. Create a users table with at least the following columns: id (primary key), username, password, email. Store passwords as hashes, never in plain text, which enhances the security of stored data.

Step 2: User Registration

Registering new users involves collecting their details (such as username, password, and email) and storing them in the database. When storing passwords, use a hashing function, such as password_hash() in PHP, which automatically applies a secure hashing algorithm and salt.

Step 3: User Login

Logging in requires the user to enter their login credentials, which are then verified against the database. Use the password_verify() function to compare the entered password with its hashed version stored in the database. Upon successful authentication, store relevant user information in the session.

Step 4: Authorization

Authorization is typically performed based on the user's role or other permissions. PHP sessions can be used to store this information and subsequently restrict access to certain parts of the application based on this data.

Step 5: Session Security

Securing sessions is crucial to prevent attacks such as session hijacking. Utilize security mechanisms such as regenerating the session ID upon login and logout, and ensuring that session data is always transmitted over a secure connection (using HTTPS).

Security Measures

• Use secure hashing functions for passwords.
• Prevent SQL injection using prepared statements when working with the database.
• Apply security principles for session management.
• Regularly update PHP and other used libraries to the latest versions.

Implementing a robust authentication and authorization system is crucial for protecting user data and the overall security of your application. By following the above steps and best practices, you'll ensure that your application is secure and resilient against common threats.