Launch Ready API security Checklist for founder landing page: Ready for customer onboarding in marketplace products?.

Launch Ready API Security Checklist for founder landing page: Ready for customer onboarding in marketplace products?

When I say "ready" for a founder landing page that drives customer onboarding in a marketplace product, I mean this: a stranger can land on the page, trust the brand, submit their details, get routed into the right onboarding flow, and not expose your API, customer data, or inbox to avoidable risk.

For this specific outcome, ready means more than "the page loads." It means the page is secure enough to collect leads or onboard users without broken auth links, exposed secrets, weak email deliverability, unsafe forms, bad redirects, or monitoring gaps that leave you blind when conversions drop. If your page cannot pass the checks below, you are not launch-ready yet.

My bar for a real launch is simple:

• No exposed secrets in frontend code or repo history.
• SPF, DKIM, and DMARC all passing.
• SSL active on every domain and subdomain.
• Redirects are intentional and tested.
• Forms and APIs reject abuse, bad input, and unauthorized access.
• Uptime monitoring exists before traffic starts.
• p95 API response time stays under 500ms for the onboarding path.
• Lighthouse performance on mobile is at least 85, with LCP under 2.5s.

Quick Scorecard

| Check | Pass criteria | Why it matters | What breaks if it fails | |---|---|---|---| | HTTPS everywhere | Main domain and subdomains force SSL with no mixed content | Protects logins and form submissions | Browser warnings, lost trust, blocked submissions | | DNS correctness | A/AAAA/CNAME records resolve correctly and point to the intended host | Prevents downtime and wrong routing | Site outage or traffic sent to stale infrastructure | | Email authentication | SPF, DKIM, and DMARC all pass on sending domain | Makes onboarding emails land in inboxes | Verification emails go to spam or fail delivery | | Secrets handling | No API keys or tokens in client code or public repo | Prevents account takeover and billing abuse | Data leak, vendor abuse, support incident | | Redirect safety | Only approved 301/302 redirects exist; no open redirect patterns | Stops phishing and broken funnel paths | Users get hijacked or bounce out of onboarding | | CORS policy | Allowed origins are explicit and minimal | Limits cross-site data exposure | Unauthorized sites call your API from browsers | | Auth checks | Protected endpoints require valid auth; no bypasses found | Protects marketplace accounts and customer data | Unauthorized access to onboarding or admin actions | | Input validation | Forms reject invalid payloads and harmful characters | Reduces injection and data corruption risk | Broken records, spam floods, downstream failures | | Rate limiting | Abuse-sensitive routes have limits per IP/user/session | Stops bot signups and credential attacks | Cost spikes, queue overload, fake accounts | | Monitoring live | Uptime alerts and error tracking are configured before launch | Lets you detect failures fast | You find outages from customers first |

The Checks I Would Run First

1. Verify there are no exposed secrets Signal: I look for API keys in frontend bundles, environment files committed to git, old deploy logs, and browser network calls that reveal private tokens.

Tool or method: I would use a repo scan plus browser devtools review. I also check secret scanners like GitHub secret scanning or TruffleHog against the repository history.

Fix path: Move every private credential into server-side environment variables. Rotate any key that was ever exposed. If a key was used in a public build once, I treat it as compromised even if it was deleted later.

2. Test auth boundaries on every onboarding endpoint Signal: Any endpoint involved in signup, invite acceptance, profile creation, payment setup, or marketplace listing creation should fail cleanly without valid auth. If I can hit it unauthenticated or as another user, that is a launch blocker.

Tool or method: I test with Postman or curl using valid sessions, expired sessions, missing tokens, and another user's token. I also try direct URL access to confirm server-side authorization exists.

Fix path: Add server-side authorization checks on every sensitive route. Do not rely on hidden buttons or frontend route guards. If the app is multi-role - buyer, seller, admin - each role needs separate permission checks.

3. Review CORS and browser-accessible API exposure Signal: The browser should only be allowed to call APIs from approved origins. Wildcard CORS on authenticated endpoints is a common mistake that turns into data exposure.

Tool or method: Inspect response headers with devtools or curl. Look for `Access-Control-Allow-Origin` values and confirm they match only your real production domains.

Fix path: Set explicit allowed origins. Avoid `*` when cookies or credentials are involved. If you do not need browser access at all for an endpoint, do not expose it cross-origin.

## Example of safer CORS intent
Access-Control-Allow-Origin: https://app.yourdomain.com
Access-Control-Allow-Credentials: true

4. Confirm email deliverability before launch traffic Signal: Welcome emails, verification links, password resets, and notification emails must pass SPF/DKIM/DMARC checks. If they fail here, your onboarding funnel loses users before they even enter the product.

Tool or method: Use MXToolbox or your email provider's diagnostics. Send test messages to Gmail and Outlook accounts and inspect authentication results.

Fix path: Publish correct DNS records for SPF and DKIM. Set DMARC to at least `p=none` during testing so you can monitor reports without breaking mail flow. Then move toward `quarantine` or `reject` once alignment is stable.

5. Measure performance on the actual onboarding path Signal: A landing page can look fine but still fail conversion because scripts block rendering or third-party tools slow form submission. For this product type I want LCP under 2.5 seconds on mobile and p95 API latency under 500ms for signup-related requests.

Tool or method: Run Lighthouse on mobile plus real-user monitoring if available. Check backend timing in logs/APM for create-account or submit-lead endpoints.

Fix path: Compress images, remove unused scripts, defer non-essential analytics until after interaction, cache static assets through Cloudflare, and profile slow database queries behind signup flows.

6. Check redirect logic end-to-end Signal: Marketplace products often use many domains - marketing site, app subdomain, auth callback URLs, help center links. One wrong redirect creates broken onboarding or phishing risk.

Tool or method: Trace all redirects with curl `-I`, browser tests across desktop/mobile paths, and manual checks for canonical domain behavior.

Fix path: Keep redirect rules explicit in Cloudflare or deployment config. Remove chained redirects where possible. Never allow user-controlled destination parameters unless they are validated against an allowlist.

Red Flags That Need a Senior Engineer

If I see any of these during review, I would stop DIY work and bring in someone who can ship safely:

1. You have multiple environments but no clear separation between staging and production secrets. 2. Your app uses cookies for auth but CORS is broad or inconsistent across subdomains. 3. The onboarding flow touches payments, invites users by email link while also creating marketplace roles. 4. You cannot explain where secrets live after deployment. 5. You have already launched once and saw fake signups, failed email delivery rates above 10 percent, broken redirects after DNS changes lower than expected uptime confidence below 99 percent.

These are not cosmetic issues.

DIY Fixes You Can Do Today

1. Remove any hardcoded keys from frontend files.

• Search your repo for `sk_`, `pk_`, `api_key`, `.env`, `secret`, `token`.
• Rotate anything suspicious immediately.

2. Turn on Cloudflare proxying for the main domain.

• Enable SSL/TLS full strict if your origin supports it.
• Turn on basic DDoS protection and caching for static assets.

3. Publish email authentication records.

• Add SPF.
• Add DKIM from your provider.
• Add DMARC with reporting enabled.

4. Test your forms like an attacker would.

• Submit empty fields.
• Submit very long strings.
• Try script tags in text inputs.
• Confirm validation happens server-side too.

5. Create one simple uptime check.

• Monitor homepage plus one onboarding endpoint every 1 minute.
• Alert by email or Slack if downtime lasts more than 2 minutes.

Where Cyprian Takes Over

Here is how checklist failures map to my Launch Ready service deliverables:

| Failure found | What I handle in Launch Ready | |---|---| | Exposed secrets or unclear env setup | Environment variables cleanup, secret handling review, rotation plan | | Broken DNS / subdomains / redirects | DNS fixes, redirect mapping, canonical domain setup | | No SSL / mixed content / weak edge protection | Cloudflare setup, SSL enforcement, caching, DDoS protection | | Email landing in spam / failing auth checks | SPF/DKIM/DMARC configuration verification | | Unmonitored launch risk / blind spots | Uptime monitoring setup plus handover checklist | | Production deployment uncertainty | Deployment review plus production release support |

Delivery window is 48 hours because this work should be treated like a controlled launch sprint:

• Hour 0-8: audit DNS, SSL, email auth, secrets, routing.
• Hour 8-24: fix critical blockers first.
• Hour 24-36: deploy production-safe changes，verify monitoring，test onboarding flow end-to-end.
• Hour 36-48: regression pass，handover checklist，launch notes，risk summary。

This is the point where buying help makes business sense instead of burning another weekend trying to guess which setting broke your funnel.

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: https://roadmap.sh/cyber-security
• OWASP Cheat Sheet Series: https://cheatsheetseries.owasp.org/
• Cloudflare Docs - SSL/TLS Overview: 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.*