API Security Best Practices for Credit Systems

When managing a credit system, security isn't optional – it's essential. A compromised credit API can lead to financial losses, user trust erosion, and legal liability. This guide covers the critical security measures every credit system should implement.

Understanding the Threat Landscape

Credit systems face unique security challenges:

• Credit theft: Unauthorized issuance or transfer
• Balance manipulation: Tampering with credit amounts
• Account takeover: Stealing user credentials
• API abuse: Excessive or malicious API usage
• Fraud rings: Coordinated abuse schemes

Authentication & Authorization

Use Strong API Keys

// Generate cryptographically secure keys
const generateApiKey = () => {
  const prefix = 'sk_live_';
  const random = crypto.randomBytes(32).toString('hex');
  return prefix + random;
};

// Store only the hash
const hashApiKey = (key) => {
  return crypto.createHash('sha256').update(key).digest('hex');
};

Implement Key Rotation

• Generate new keys periodically
• Support multiple active keys during transition
• Revoke old keys after grace period
• Log all key usage for audit

Scope API Keys

Limit what each key can do:

const keyScopes = {
  read_only: ['balance.read', 'transactions.list'],
  standard: ['balance.read', 'credits.issue', 'credits.deduct'],
  admin: ['*']
};

Request Validation

Validate All Inputs

Never trust client data:

const validateIssueRequest = (body) => {
  const schema = {
    user_id: { type: 'string', required: true, maxLength: 255 },
    amount: { type: 'number', required: true, min: 1, max: 1000000 },
    reason: { type: 'string', maxLength: 500 }
  };
  
  return validate(body, schema);
};

Use Idempotency Keys

Prevent duplicate operations:

app.post('/credits/issue', async (req, res) => {
  const idempotencyKey = req.headers['x-idempotency-key'];
  
  // Check if this request was already processed
  const existing = await redis.get(`idempotency:${idempotencyKey}`);
  if (existing) {
    return res.json(JSON.parse(existing));
  }
  
  const result = await issueCredits(req.body);
  
  // Store result for future duplicate requests
  await redis.setex(`idempotency:${idempotencyKey}`, 86400, JSON.stringify(result));
  
  return res.json(result);
});

Rate Limiting

Implement Tiered Limits

const rateLimits = {
  anonymous: { requests: 10, window: '1m' },
  authenticated: { requests: 100, window: '1m' },
  premium: { requests: 1000, window: '1m' }
};

Use Sliding Windows

More accurate than fixed windows:

const checkRateLimit = async (userId, limit, windowMs) => {
  const key = `ratelimit:${userId}`;
  const now = Date.now();
  
  // Remove old entries
  await redis.zremrangebyscore(key, 0, now - windowMs);
  
  // Count requests in window
  const count = await redis.zcard(key);
  
  if (count >= limit) {
    return { allowed: false, retryAfter: windowMs / 1000 };
  }
  
  // Add this request
  await redis.zadd(key, now, `${now}:${crypto.randomUUID()}`);
  await redis.expire(key, windowMs / 1000);
  
  return { allowed: true, remaining: limit - count - 1 };
};

Fraud Detection

Monitor Anomalies

Watch for suspicious patterns:

• Sudden spikes in issuance
• Unusual deduction patterns
• Geographic anomalies
• Velocity violations

const detectFraud = async (transaction) => {
  const checks = [
    checkVelocity(transaction),
    checkGeolocation(transaction),
    checkDeviceFingerprint(transaction),
    checkUserBehavior(transaction)
  ];
  
  const results = await Promise.all(checks);
  const riskScore = calculateRiskScore(results);
  
  if (riskScore > 0.8) {
    await flagForReview(transaction);
    return { blocked: true, reason: 'High risk score' };
  }
  
  return { blocked: false };
};

Implement Velocity Checks

const velocityRules = {
  maxIssuePerHour: 10000,
  maxDeductPerMinute: 100,
  maxTransactionsPerUser: 50
};

Data Protection

Encrypt Sensitive Data

// Encrypt at rest
const encryptBalance = (balance) => {
  return crypto.publicEncrypt(publicKey, Buffer.from(String(balance)));
};

// Use TLS for transit
// Require HTTPS for all API endpoints

Implement Audit Logging

Log everything:

const auditLog = async (event) => {
  await db.auditLogs.insert({
    timestamp: new Date(),
    actor: event.userId,
    action: event.action,
    resource: event.resource,
    metadata: event.metadata,
    ip: event.ip,
    userAgent: event.userAgent
  });
};

Webhook Security

Verify Signatures

const verifyWebhookSignature = (payload, signature, secret) => {
  const expectedSig = crypto
    .createHmac('sha256', secret)
    .update(payload)
    .digest('hex');
  
  return crypto.timingSafeEqual(
    Buffer.from(signature),
    Buffer.from(expectedSig)
  );
};

Security Checklist

• API keys are hashed before storage
• All endpoints require authentication
• Input validation on all parameters
• Rate limiting is implemented
• Idempotency keys are supported
• HTTPS is enforced
• Webhook signatures are verified
• Audit logs are maintained
• Anomaly detection is active
• Regular security audits are scheduled

Incident Response

Have a plan for security incidents:

1. Detect: Monitor for suspicious activity
2. Contain: Isolate affected systems
3. Investigate: Determine scope and cause
4. Remediate: Fix vulnerabilities
5. Communicate: Notify affected users
6. Review: Update processes to prevent recurrence

Conclusion

Security is an ongoing process, not a one-time implementation. By following these best practices, you can build a credit system that protects your users and your business.

Review your security settings in the dashboard.