I'm building a fintech API and need request inspection

Absolutely — request inspection is a great fit for a fintech API, especially for fraud detection, compliance, rate limiting, and debugging.

Here’s a practical way to think about it.

What “request inspection” can mean

You may want to inspect requests for:

• Authentication/authorization issues
• Schema validation
• Fraud/risk signals
• PII/PCI detection
• Replay or abuse patterns
• Client/device fingerprinting
• Unexpected headers/query/body content
• Request tracing and audit logging

Recommended inspection points

Inspect at multiple layers:

1. Before parsing body

   • IP, TLS info, method, path, headers, content-length, user-agent
   • Detect malformed or suspicious requests early

2. After parsing

   • Validate JSON/XML/form fields against schema
   • Check required fields, formats, enum values, ranges

3. Business-rule layer

   • Amount thresholds
   • Country/currency mismatch
   • Velocity checks
   • Suspicious beneficiary/account patterns

4. Post-processing / logging

   • Store minimal safe audit trail
   • Redact secrets and sensitive fields

Fintech-specific checks

Useful checks include:

• Header anomalies
  • Missing Authorization
  • Invalid Idempotency-Key
  • Unexpected Content-Type
• Payload validation
  • Amount precision rules
  • Negative or zero values where disallowed
  • Duplicate transaction IDs
• Risk signals
  • High request rate
  • New device/IP
  • Geolocation mismatch
  • Unusual time-of-day activity
• Compliance
  • Detect PAN, CVV, SSN, bank account numbers in logs or requests
  • Ensure PII is not echoed back or stored unsafely

Example inspection pipeline

A typical pipeline:

1. Edge gateway
   • IP reputation, WAF rules, rate limiting
2. Auth service
   • Verify token, scopes, mTLS, signatures
3. Validation service
   • JSON schema + semantic validation
4. Risk engine
   • Scores request based on behavior/context
5. Audit logger
   • Redacted structured logs + trace IDs

Example fields to log safely

Log:

• request ID
• timestamp
• endpoint
• method
• status code
• latency
• authenticated tenant/user ID
• risk score
• decision reason codes

Avoid logging raw:

• passwords
• tokens
• CVV
• full PAN
• secrets
• private keys
• full bank account details

Example redaction rules

If you inspect JSON bodies, redact:

• password
• token
• authorization
• cvv
• pan
• ssn
• account_number
• iban
• secret

Quick architecture suggestion

If you’re building this in production, I’d recommend:

• API gateway for coarse inspection
• Middleware in the app for request validation/redaction
• Dedicated risk service for scoring
• Central audit pipeline with strict access controls

Example pseudo-logic

if request is malformed:
    reject 400

if auth invalid:
    reject 401/403

if schema invalid:
    reject 422

risk = score(request)

if risk >= block_threshold:
    reject 403

log redacted request metadata
continue

Important fintech cautions

• Never log secrets or raw payment data
• Use field-level encryption where needed
• Ensure logs meet retention and access-control policies
• Treat inspection data as sensitive too
• If you handle cards, consider PCI DSS boundaries carefully

If you want, I can help you design:

1. a request inspection middleware,
2. a risk-scoring schema,
3. or a safe logging/redaction spec for your fintech API.