How to use API key in cURL for authentication

API keys provide a unique credential for identifying and authorizing clients requesting resources from a server. Servers commonly rely on a API key embedded in a HTTP request to verify that the client is permitted to access protected endpoints. Tools such as cURL seamlessly integrate these keys by placing them into headers or query parameters for secure and authorized resource retrieval.

When interacting with various services, passing the API key through an Authorization header ensures the server recognizes the request as valid and trusted. Using cURL enables automatic inclusion of the key, preventing unauthorized access to data or restricted functionality. This approach promotes data integrity, robust security, and consistent performance.

In production or development environments, API keys must remain confidential to avoid exposure. Storing them in environment variables or encrypted vaults reduces accidental leakage in scripts or logs. Combined with careful handling in cURL commands, these practices establish a reliable and secure foundation for interacting with protected web APIs.

1. Open a terminal.
2. Send a HTTP request and include the API key in the Authorization header.

   $ curl --header "Authorization: ApiKey YOUR_API_KEY" "https://www.example.com/api/data"
   {
     "data": "sample response"
   }

   Replace YOUR_API_KEY with the actual key. Using Z--header adds the key to the request’s headers.

3. Include the API key as a query parameter if required.

   $ curl "https://www.example.com/api/data?api_key=YOUR_API_KEY"
   {
     "data": "sample response"
   }

   Use this approach only if the API explicitly requires the key as a query parameter.

4. Store the API key in an environment variable and reference it securely.

   $ export API_KEY="YOUR_API_KEY"
   $ curl --header "Authorization: ApiKey $API_KEY" "https://www.example.com/api/data"
   {
     "data": "sample response"
   }

   Keeping the API key in an environment variable reduces exposure in command histories.

5. Use Z--verbose to verify request and response details.

   $ curl --header "Authorization: ApiKey YOUR_API_KEY" "https://www.example.com/api/data" --verbose
   > GET /api/data HTTP/1.1
   > Authorization: ApiKey YOUR_API_KEY
   < HTTP/1.1 200 OK
   {
     "data": "sample response"
   }

   Z--verbose shows detailed request and response information.

6. Check response codes for errors.

   $ curl --header "Authorization: ApiKey YOUR_API_KEY" "https://www.example.com/api/data" --verbose
   < HTTP/1.1 401 Unauthorized

   HTTP 401 or 403 indicate invalid or insufficient permissions for the given API key.

7. Unset or overwrite the environment variable when no longer needed.

   $ unset API_KEY

   Protect the API key at all times to prevent unauthorized access.