How to use bearer token for authentication in cURL

Bearer Tokens are commonly used in API authentication, especially within OAuth 2.0 protocols. These tokens provide secure access to protected resources by including them in the Authorization header of HTTP requests. Instead of sending user credentials, the Bearer Token is passed in each request, allowing for secure and repeated access.

To obtain a Bearer Token, a client typically sends a request to the authentication provider using client credentials such as a client ID and secret. Once acquired, the token can be used in subsequent API requests. It must be included in the request header and can be refreshed as necessary when it expires.

cURL makes it easy to incorporate Bearer Tokens into your requests. With its built-in features, you can pass the token in the header, manage multiple tokens, and store them securely for reuse. It also supports refreshing expired tokens, ensuring continuous access without manual intervention. These features simplify the process of managing API authentication.

1. Open the terminal.
2. Acquire the Bearer Token from the authentication provider.

   $ curl -d "client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET&grant_type=client_credentials" https://auth.example.com/oauth/token
   
   {
     "access_token": "YOUR_ACCESS_TOKEN",
     "token_type": "Bearer",
     "expires_in": 3600
   }

   Replace YOUR_CLIENT_ID and YOUR_CLIENT_SECRET with actual values. The response will include the Bearer Token.

3. Include the Bearer Token in the Authorization header of your cURL request.

   $ curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://api.example.com/data
   
   {
     "data": "sample data response"
   }

   Use the -H or --header option to include the Authorization header. The Bearer Token should be prefixed with Bearer followed by a space.

4. Use verbose mode to view the full request and response for debugging.

   $ curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://api.example.com/data -v
   
   *   Trying 123.45.67.89...
   * Connected to api.example.com (123.45.67.89) port 443 (#0)
   > GET /data HTTP/1.1
   > Host: api.example.com
   > Authorization: Bearer YOUR_ACCESS_TOKEN
   > User-Agent: curl/7.68.0
   > Accept: */*
   < HTTP/1.1 200 OK
   < Content-Type: application/json
   < {"data": "sample data response"}

   The -v or --verbose option provides detailed information about the request and response, which can be useful for troubleshooting authentication issues.

5. Store the Bearer Token in a secure location.

   $ echo "Authorization: Bearer YOUR_ACCESS_TOKEN" > .bearer_token

   Storing tokens in a file helps manage different environments or user tokens efficiently. Ensure this file is stored securely to prevent unauthorized access.

6. Refresh the Bearer Token when it expires.

   $ curl -d "client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET&grant_type=refresh_token&refresh_token=YOUR_REFRESH_TOKEN" https://auth.example.com/oauth/token
   
   {
     "access_token": "NEW_ACCESS_TOKEN",
     "token_type": "Bearer",
     "expires_in": 3600
   }

   Bearer Tokens often expire after a certain period. Use the refresh token endpoint to obtain a new access token when necessary.

7. Load the Authorization header from a file for easier management.

   $ curl -K .bearer_token https://api.example.com/data
   
   {
     "data": "sample data response"
   }

   Loading headers from a file simplifies the management of complex requests and ensures consistency across requests.