Secure API Architecture for Fintech

Documentation That Prevents Breaches

In fintech, your API is your product. Here's how to design APIs that are both developer-friendly AND secure.

The Security-First Approach

Every endpoint should answer these questions:

1. Who can access this? (Authentication)
2. What can they do? (Authorization)
3. How much can they do? (Rate limiting)
4. What data is exposed? (Data minimization)

API Security Checklist

# OpenAPI Security Specification
security:
  - bearerAuth: []  # JWT required
  - apiKey: []      # API key backup

paths:
  /v1/transactions:
    post:
      security:
        - bearerAuth: []
      x-rate-limit:
        requests: 100
        window: 60  # seconds
      responses:
        '201':
          description: Transaction created
        '429':
          description: Rate limit exceeded

Documentation Best Practices

1. OpenAPI/Swagger - Machine-readable spec
2. Examples for every endpoint - Copy-paste ready
3. Error code catalog - What went wrong, how to fix
4. Changelog - Version history with breaking changes
5. Security notes - What's PII, what's encrypted

Tools We Use

• Swagger UI - Interactive documentation
• Postman Collections - Runnable examples
• AsyncAPI - For webhooks and events
• Redoc - Beautiful static docs

Good documentation is a security feature.