API Key Authentication is a simple and widely used method to secure APIs. The client sends a unique API key with each request, allowing the server to identify and authorize the client.
? Key Concepts
API Key is a unique secret token issued to a client
Used for authentication and basic authorization
Commonly sent via HTTP headers or query parameters
Easy to implement but less secure than OAuth or JWT
? Syntax / Theory
There are two common ways to send an API key:
Header Method – API key is sent in request headers
Query Parameter Method – API key is appended to the URL
? Code Examples
? View Code Example
// API Key authentication using HTTP headers
GET /api/users HTTP/1.1
Host: example.com
X-API-KEY: your_api_key_here
? View Code Example
// API Key authentication using query parameters
GET /api/users?api_key=your_api_key_here HTTP/1.1
Host: example.com
? Live Output / Explanation
Server Behavior
The server validates the API key. If valid, it processes the request. If invalid or missing, it returns an error such as 401 Unauthorized.
? Interactive Example
In Postman:
Select the request method (GET/POST)
Go to Headers tab and add the API key
Or append the API key as a query parameter in the URL
Send the request and observe the response
? Live Simulator
Test authentication below. The correct key is SECRET-123.
? Use Cases
Public APIs with rate limiting
Internal service-to-service communication
Developer access to third-party APIs
Basic authentication for microservices
? Tips & Best Practices
Always prefer header-based API keys
Never expose API keys in frontend code
Rotate API keys periodically
Use HTTPS to protect API keys in transit
? Try It Yourself
Create a simple API endpoint that checks an API key
Test the endpoint using Postman with headers
Try sending an invalid API key and observe the response