In the modern world of web development, developing frontend and backend applications separately provides freedom and flexibility, but also brings serious security risks. If necessary precautions are not taken between these two parties communicating via REST API, serious problems such as data leakage, identity theft, and system breaches may occur. In this article, we will explain the security improvements that need to be made when using REST API in systems where frontend and backend are coded separately, from A to Z.

Why are Frontend and Backend Coded Separately?

Independent development of both sides
Using the same backend for mobile and web applications
Better performance and scalability
Separation of teams according to their areas of expertise

However, this structure necessitates that separately operating systems can communicate in a healthy and secure manner.

Most Common Security Mistakes When Using REST API

API endpoints not performing correct validation
Not using encrypted (HTTPS) connection
Allowing unauthorized access (lack of Authorization)
Not implementing Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF) protection
Not applying rate limit (vulnerability to attacks)
Disclosing unnecessary data (Overexposure)

How to Ensure REST API Security in Frontend-Backend Separation?

1. Do Not Publish API Without Using HTTPS

All data between your server and clients must be encrypted over HTTPS.
Use an SSL/TLS certificate. You can prefer free options such as Let's Encrypt.

2. Establish Authentication and Authorization Mechanism

Use secure token-based systems such as JWT (JSON Web Token) or OAuth2.
Make authentication mandatory for each request before accessing the API.

3. Apply Rate Limiting and IP-Based Restriction

Limit the number of API requests a user can make within a certain period.
Automatically blacklist IP addresses that make too many requests.

4. Adopt the Principle of Minimum Information in Data Transmission

Return only the information that the frontend needs.
Do not include unnecessary fields (password hash, internal IDs, etc.) in the API response.

5. Configure CORS Settings Correctly

The API should only allow requests from specific domains.
Specify a specific domain instead of making the "Access-Control-Allow-Origin" value "*".

6. Perform Data Validation

Create a control mechanism that validates all incoming data on the server.
Use validation systems that will take precautions against attacks such as SQL Injection and XSS.

7. Protect API Keys and Secret Information

API keys should never be in the frontend code.
API keys should be stored on the server side and only temporary tokens should be given to the user.

8. Record User Requests and API Traffic

You can detect security breaches early by logging all API requests and errors.
Be compliant with data protection laws such as KVKK and GDPR when storing logs.

9. Manage Sessions Healthily

Keep user token durations short.
Use refresh token logic.
Track active sessions against token theft.

10. Add Protection Against Cross-Site Hazards

Use CSRF token.
Sanitize all data sent for XSS protection.

Extra Recommendations

Integrate two-factor authentication (two-factor authentication) especially in sensitive endpoints.
Close old and insecure endpoints by versioning the API.
Subject every 3rd party library and service to security tests before using it.

Conclusion: Security Should Be a Priority From Day One

Systems that develop frontend and backend separately and communicate with REST API become more modular, more flexible and more scalable. However, in order for this flexibility to increase productivity, you must focus on security from the beginning. If you apply the technical recommendations here, you can make your REST APIs a much more secure and performant structure.