API Integration Services Checklist for SaaS and Ecommerce Platforms

Every modern SaaS or e-commerce platform is essentially a hub of third-party API integrations. Stripe for billing, SendGrid for emails, Twilio for SMS, Salesforce for CRM, Algolia for search, AWS S3 for files. Each of these integrations is a potential point of failure that can take your entire application down if not designed robustly.

Use this checklist before implementing any new third-party API integration to ensure reliability and observability from day one.

1. Authentication and Credential Management

• API Keys in Environment Variables: Never hardcode API keys in the source code. Store all keys in environment variables (.env file locally, AWS Secrets Manager or Doppler in production). Rotate keys quarterly.
• OAuth 2.0 Token Storage: For integrations that use OAuth (like Google, Salesforce, or QuickBooks), the access token and refresh token must be stored encrypted in your database per user account, never in a server-side global variable.
• Scoped Credentials: When creating API keys for third-party services, use the minimum required permissions (the "Principle of Least Privilege"). If you only need to read data, do not use a key with write permissions.

2. Request Design and Rate Limiting

• Idempotency Keys: For mutation operations (creating a payment, sending an email), always use the payment provider's idempotency key mechanism. This ensures that if a network timeout causes your code to retry the request, the third-party service processes it only once, preventing duplicate charges.
• Rate Limit Handling: Every API has rate limits. Your integration must detect 429 Too Many Requests responses and implement an exponential backoff retry strategy (wait 1 second, then 2, then 4, then 8...) before giving up.
• Timeouts: Set explicit HTTP request timeouts on every outbound API call (e.g., 10 seconds maximum). Without a timeout, a slow third-party API can cause your server's connection pool to exhaust, taking down your entire application for all users.

3. Webhook Security

Webhooks (where the third-party sends data to your server) are a critical attack vector if not secured properly.

• Signature Verification: Every major API provider (Stripe, GitHub, Shopify) signs its webhooks with a secret. Your webhook receiver must verify this signature cryptographically before trusting and processing the payload. A webhook that skips signature verification can be spoofed by any attacker.
• Idempotent Processing: Webhooks can be delivered more than once. Your handler must check if the event ID has already been processed (by storing it in a database) and skip duplicates gracefully.
• Immediate 200 Response: Return a 200 OK response to the webhook sender immediately upon receipt. Then process the event in a background queue. Never perform slow database operations synchronously in the webhook HTTP handler—the provider will time out and retry.

4. Error Handling and Observability

• Log Every API Call: Log the request payload, the response code, and the response body for every outbound API call. Store these in your structured logging system (e.g., send to a Datadog or CloudWatch log stream). This is invaluable for debugging billing disputes or integration failures.
• Alert on Integration Failures: Configure Sentry or your monitoring tool to alert you specifically when a critical API integration fails (e.g., "Stripe payment charge failed"). Do not let these silently disappear into a log file.
• Circuit Breaker Pattern: If a third-party service is down, your integration should "open the circuit" after a threshold of consecutive failures (e.g., 5 failed attempts) and stop trying for a cooldown period (e.g., 60 seconds), preventing your app from piling up failed requests against an unavailable service.

Reliable API integrations are the backbone of any modern digital product. If you need an experienced developer to architect and build robust third-party integrations, visit my backend API development page to discuss your project.