Follow the steps below.

Validate input

The first step to secure a back-end application is to validate the input that comes from the user or other sources. Validation means checking that the input is in the expected format, type, and range, and that it does not contain any malicious code or commands. You can use built-in functions, libraries, or frameworks to perform validation, depending on the back-end language and framework you are using. For example, in PHP, you can use filter_var() to sanitize and validate input, or in Express.js, you can use middleware like express-validator to validate and sanitize input.

Sanitize output

The second step to secure a back-end application is to sanitize the output that goes to the user or other systems. Sanitization means removing or escaping any characters or symbols that could be interpreted as code or commands by the browser or the database. This prevents cross-site scripting (XSS) attacks, which exploit the ability of attackers to inject malicious scripts into web pages. You can use built-in functions, libraries, or frameworks to sanitize output, depending on the back-end language and framework you are using. For example, in PHP, you can use htmlspecialchars() to escape HTML characters, or in Express.js, you can use middleware like helmet to set HTTP headers that prevent XSS attacks.

Encrypt data

The third step to secure a back-end application is to encrypt the data that is stored or transmitted. Encryption means converting the data into a form that can only be read by authorized parties who have the key or the password. This prevents unauthorized access, modification, or theft of the data. You can use built-in functions, libraries, or frameworks to encrypt data, depending on the back-end language and framework you are using. For example, in PHP, you can use openssl_encrypt() to encrypt data with a secret key, or in Express.js, you can use middleware like bcrypt to hash passwords before storing them in the database.

Implement authentication

The fourth step to secure a back-end application is to implement authentication. Authentication means verifying the identity of the user or the system that is accessing the back-end application. This prevents unauthorized or impersonated access to the back-end application. You can use built-in functions, libraries, or frameworks to implement authentication, depending on the back-end language and framework you are using. For example, in PHP, you can use session_start() to create and manage sessions for logged-in users, or in Express.js, you can use middleware like passport to authenticate users with various strategies, such as local, OAuth, or JWT.

Authorize access

The fifth step to secure a back-end application is to authorize access. Authorization means granting or denying access to specific resources or actions based on the role or permission of the user or the system. This prevents unauthorized or inappropriate access to the back-end application. You can use built-in functions, libraries, or frameworks to authorize access, depending on the back-end language and framework you are using. For example, in PHP, you can use $_SESSION to store and check the role or permission of the user, or in Express.js, you can use middleware like express-acl to enforce access control lists based on the role or permission of the user.

Monitor and update

The sixth and final step to secure a back-end application is to monitor and update. Monitoring means keeping track of the performance, activity, and errors of the back-end application. Updating means applying patches, fixes, and upgrades to the back-end application. This prevents performance issues, security breaches, and vulnerabilities in the back-end application. You can use tools, services, or frameworks to monitor and update, depending on the back-end language and framework you are using. For example, in PHP, you can use tools like PHP Monitor or PHP Error to monitor and debug the back-end application, or in Express.js, you can use services like NPM Audit or Snyk to scan and update the dependencies of the back-end application.