Launch Ready API security Checklist for mobile app: Ready for security review in marketplace products?.

What "ready" means for a marketplace mobile app security review

For a marketplace mobile app, "ready" means the app can survive a real security review without exposing customer data, seller data, payment flows, or admin access. It also means the API does not trust the mobile client, because mobile apps are easy to reverse engineer and tamper with.

If I were self-assessing this product, I would want to see all of this before launch:

• No exposed secrets in the app bundle, repo, logs, or CI output.
• Auth is enforced on every sensitive endpoint.
• Authorization is object-level, not just "user is logged in."
• Rate limits exist on login, OTP, password reset, search, messaging, and upload endpoints.
• CORS is locked down.
• Production uses HTTPS only with valid SSL.
• DNS, email authentication, and monitoring are already working.
• p95 API latency is under 500ms for core flows like login, browse listings, create listing, checkout, and messaging.

For marketplace products, the failure mode is usually not one big hack. It is small gaps that add up to account takeover, seller impersonation, data scraping, spam listings, refund abuse, and support overload.

Quick Scorecard

| Check | Pass criteria | Why it matters | What breaks if it fails | |---|---|---|---| | Authentication | All protected endpoints require valid auth tokens | Prevents anonymous access to user data | Data leaks and unauthorized actions | | Authorization | Object-level checks on every listing, order, chat, payout action | Stops users from touching other users' records | Account takeover impact grows fast | | Secrets handling | Zero secrets in mobile code or public repos | Mobile apps can be decompiled | API keys get stolen and abused | | Rate limiting | Login, OTP, reset, search, upload have limits | Blocks brute force and scraping | Fraud spikes and service abuse | | Input validation | Server validates all request fields and file uploads | Mobile clients cannot be trusted | Injection bugs and bad data enter system | | CORS policy | Only approved origins allowed; no wildcard with credentials | Reduces browser-based abuse paths | Token leakage and cross-site abuse | | Transport security | HTTPS only; HSTS enabled; valid SSL everywhere | Protects credentials in transit | Interception risk and app trust issues | | Logging hygiene | No tokens, passwords, PII in logs or crash reports | Logs become attack surface too | Secret exposure through support tools | | Monitoring alerts | Uptime checks plus error rate alerts exist | You need to know before users do | Silent downtime burns ad spend | | Email auth | SPF, DKIM, DMARC all pass for domain email | Prevents spoofed marketplace emails | Phishing risk and deliverability problems |

A good target for a launch-ready marketplace API is p95 under 500ms for core authenticated endpoints and zero critical auth bypasses in testing.

The Checks I Would Run First

1. Authorization on every object

• Signal: A logged-in user can fetch or modify another user's listing by changing an ID in the request.
• Tool or method: Manual API testing with Postman or Insomnia plus direct replay of requests from logs or proxy capture.
• Fix path: Add server-side ownership checks on every read/write/delete route. Do not rely on hidden fields in the mobile UI.

2. Secret exposure in app bundles and repos

• Signal: API keys, private tokens, Firebase keys with privileged access, S3 keys, or Stripe secret keys appear in source code or build artifacts.
• Tool or method: Search the repo with `git grep`, scan compiled bundles with strings extraction tools, check CI logs and environment files.
• Fix path: Move all secrets to server-side environment variables. Rotate anything that was ever committed. Assume exposure if it shipped once.

3. Broken auth flow under tampering

• Signal: The app accepts expired tokens, malformed JWTs, reused reset links, or missing session checks.
• Tool or method: Proxy the mobile traffic through Charles Proxy or Burp Suite and mutate headers and payloads.
• Fix path: Enforce token expiry checks server-side. Validate issuer/audience/signature. Reject missing or stale sessions.

4. Rate limit gaps on high-risk endpoints

• Signal: Login can be brute forced. OTP can be guessed. Search can be scraped at high volume. Uploads can be spammed.
• Tool or method: Send repeated requests at controlled volume from one IP and one account; watch for lockouts or throttling.
• Fix path: Add IP-based and account-based rate limits with sensible thresholds. For example: 5 login attempts per minute per account plus device/IP throttles.

5. CORS and cookie policy

• Signal: `Access-Control-Allow-Origin: *` appears with credentialed requests or sensitive APIs are callable from untrusted web origins.
• Tool or method: Inspect response headers from production endpoints with browser devtools or curl.
• Fix path: Use an allowlist of exact origins. If you use cookies for auth, set `Secure`, `HttpOnly`, and `SameSite` correctly.

6. Logging and monitoring blind spots

• Signal: Failures are invisible until a founder notices angry users. Logs contain tokens or PII.
• Tool or method: Trigger a failed login deliberately and inspect logs; verify uptime monitoring hits production every minute.
• Fix path: Strip secrets from logs. Add alerts for 5xx spikes, auth failures above baseline, queue backlogs if used for media processing.

Set-Cookie: session=abc123; Secure; HttpOnly; SameSite=Lax

That one line matters because if your session cookie is readable by JavaScript or sent too broadly across sites, you have created avoidable account theft risk.

Red Flags That Need a Senior Engineer

1. The mobile app talks directly to third-party services with privileged keys

• If the client holds powerful credentials anywhere outside the backend boundary, I would stop there.

2. Marketplace roles are fuzzy

• If buyers can become sellers through one weak endpoint change while admins use the same API surface as regular users, authorization is probably broken somewhere.

3. You have no way to rotate secrets quickly

• If an exposed key would take days to replace across environments and builds, you do not have operational control yet.

4. You are using custom auth without tests

• Homemade JWT logic works right up until it does not. One bad refresh flow can break every active session.

5. You cannot reproduce production locally

• If staging differs from prod in DNS setup, email auth status, env vars, Cloudflare rules, or storage permissions too much to test safely at home base-level fidelity is missing.

DIY Fixes You Can Do Today

1. Inventory every secret

• List API keys,, webhook secrets,, database URLs,, OAuth client secrets,, SMTP credentials,, analytics tokens,,and push notification credentials.
• Rotate anything that has ever lived in public code,, shared docs,, screenshots,,or chat threads.

2. Lock down your auth routes

• Review login,, signup,, password reset,, OTP,,and refresh token endpoints first.
• Make sure failed attempts return generic errors so you do not leak whether an account exists.

3. Check your CORS settings

• Remove wildcards unless the endpoint is truly public.
• If you use cookies,, make sure credentialed requests only work from approved domains.

4. Turn on basic protection at the edge

• Put Cloudflare in front of your domain.
• Enable SSL enforcement,, DDoS protection,, caching for static assets,,and bot filtering where appropriate.

5. Verify email deliverability before launch

• Set SPF,, DKIM,,and DMARC on your domain email now.
• This reduces spoofing risk and prevents your verification emails from landing in spam during onboarding.

Where Cyprian Takes Over

Here is how checklist failures map to delivery:

| Checklist failure | What I fix in Launch Ready | Timeline | |---|---|---| | Secrets exposed or unmanaged env vars | Move secrets to secure environment variables,,,rotate exposed values,,,confirm production config hygiene | Hour 0-8 | | Weak domain/email setup | DNS setup,,,redirects,,,subdomains,,,SSL,,,SPF/DKIM/DMARC verification | Hour 0-12 | | No edge protection | Cloudflare setup,,,caching rules,,,DDoS protection,,,basic firewall rules where needed | Hour 6-16 | | Deployment risk / broken prod release | Production deployment checks,,,rollback-safe handover steps,,,build verification || Hour 8-24 | | Missing monitoring || Uptime monitoring setup,,,alert routing,,,basic incident checklist || Hour 12-24 | | Security review blockers || Review of auth surface,,,,rate limits,,,,CORS,,,,logging,,,,handover notes || Hour 18-36 |

My goal is simple: by hour 48 you have a live domain,,,,working email authentication,,,,production deployment,,,,secured secrets handling,,,,monitoring,,,,and a handover checklist you can actually use without guessing what broke later.

If your marketplace app already has traffic running through ads,,,,I care even more about this order because broken trust costs money fast: 1. Stop leaks. 2. Stabilize deployment. 3. Harden API security basics. 4. Then scale acquisition.

Delivery Map

References

• roadmap.sh Code Review Best Practices: https://roadmap.sh/code-review-best-practices
• roadmap.sh API Security Best Practices: https://roadmap.sh/api-security-best-practices
• roadmap.sh Cyber Security Roadmap: https://roadmap.sh/cyber-security
• OWASP API Security Top 10: https://owasp.org/www-project-api-security/
• Cloudflare SSL/TLS documentation: https://developers.cloudflare.com/ssl/

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Take the next step

If this is a problem in your product right now, here is what to do next:

• [Use the free Cyprian tools](/tools) - estimate cost, score app risk, check launch readiness, or pick the right service sprint.

• [Book a discovery call](/contact) - I will tell you honestly whether you need a sprint or if you can DIY the next step.

*Written by Cyprian Tinashe Aarons - senior full-stack and AI engineer helping founders rescue, launch, automate, and scale AI-built products.*