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Building API Authentication from Scratch: A Practical Guide

By Neo13 min read
AuthenticationAPI SecurityPythonFastAPIBackend
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Table of Contents

  • Why Build Your Own?
  • Design Goals
  • 1. API Key Format
  • 2. Storage Format
  • 3. Security Requirements
  • 4. Rate Limiting Tiers
  • 5. Middleware Architecture
  • Implementation: Step by Step
  • Step 1: API Key Generation
  • Step 2: Key Hashing
  • Step 3: Key Storage & Loading
  • Step 4: Rate Limiting
  • Step 5: FastAPI Middleware
  • Step 6: Using Auth in Endpoints
  • Testing the Implementation
  • Test 1: Protected Endpoint Without Key
  • Test 2: Invalid API Key
  • Test 3: Valid Key Within Rate Limit
  • Test 4: Rate Limit Exceeded
  • Test 5: Public Endpoints (No Auth)
  • Security Best Practices
  • 1. Constant-Time Comparison
  • 2. API Key Rotation
  • 3. Audit Logging
  • 4. Environment-Specific Configuration
  • Monitoring & Observability
  • Key Metrics to Track
  • Alerts to Set Up
  • Complete Code
  • Lessons Learned
  • 1. Middleware > Decorators
  • 2. Rate Limiting is Essential
  • 3. Good Error Messages Matter
  • 4. Headers Communicate State
  • What's Next?
  • Conclusion
  • Resources

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