Introduction:

Welcome to a quick guide on enhancing your API testing workflow in Postman! If you frequently work with APIs that require OAuth tokens, you know the hassle of manually refreshing tokens. This blog post will show you how to automate this process using Pre-request scripts in Postman.

What You Need:

  • Postman installed on your system.
  • API credentials (Client ID, Client Secret) for the OAuth token endpoint.

Step 1: Setting Up Your Environment

  • Open Postman and select your workspace.
  • Go to the ‘Environments’ tab and create a new environment (e.g., “MyAPIEnvironment”).
  • Add variables like accessToken, clientId, clientSecret, and tokenUrl.

Step 2: Creating the Pre-request Script

  • Go to the ‘Pre-request Scripts’ tab in your request or collection.
  • Add the following JavaScript code:
if (!pm.environment.get('accessToken') || pm.environment.get('isTokenExpired')) {
    const getTokenRequest = {
        url: pm.environment.get('tokenUrl'),
        method: 'POST',
        header: 'Content-Type:application/x-www-form-urlencoded',
        body: {
            mode: 'urlencoded',
            urlencoded: [
                { key: 'client_id', value: pm.environment.get('clientId') },
                { key: 'client_secret', value: pm.environment.get('clientSecret') },
                { key: 'grant_type', value: 'client_credentials' }
            ]
        }
    };

    pm.sendRequest(getTokenRequest, (err, res) => {
        if (err) {
            console.log(err);
        } else {
            const jsonResponse = res.json();
            pm.environment.set('accessToken', jsonResponse.access_token);
            pm.environment.set('isTokenExpired', false);
        }
    });
}

Step 3: Using the Access Token in Your Requests

  • In the ‘Authorization’ tab of your API request, select ‘Bearer Token’ as the type.
  • For the token, use the {{accessToken}} variable.

Step 4: Testing and Verification

  • Send your API request.
  • The Pre-request script should automatically refresh the token if it’s not set or expired.
  • Check the Postman Console to debug or verify the token refresh process.

Conclusion: Automating token refresh in Postman saves time and reduces the error-prone process of manual token updates. With this simple Pre-request script, your OAuth token management becomes seamless, letting you focus more on testing and less on token management.

Further Reading: