Launch Ready API security Checklist for AI-built SaaS app: Ready for customer onboarding in marketplace products?.

Launch Ready API security Checklist for AI-built SaaS app: Ready for customer onboarding in marketplace products?

"Ready" does not mean the app runs on your laptop or that a demo flow works once. For an AI-built SaaS app aimed at customer onboarding in a marketplace product, ready means a new user can sign up, verify access, connect the right account, and complete onboarding without exposing secrets, leaking data across tenants, or breaking email delivery.

I would call it launch-ready only if these are true:

• No critical auth bypasses.
• Zero exposed secrets in code, logs, or frontend bundles.
• Customer data is isolated by tenant, workspace, or account.
• Signup and onboarding emails reliably land in inboxes, not spam.
• p95 API latency is under 500 ms for core onboarding endpoints.
• Cloudflare, SSL, redirects, and monitoring are already in place.
• Failed requests are observable before customers report them.

If any of those fail, you do not have a launch problem. You have a customer trust problem, a support load problem, and possibly a security incident waiting to happen.

Quick Scorecard

| Check | Pass criteria | Why it matters | What breaks if it fails | |---|---|---|---| | Authentication | Login and session flow block unauthorized access | Prevents account takeover and tenant abuse | Users see other users' data or get into paid areas free | | Authorization | Every API route checks role and tenant scope | Stops cross-account data exposure | One customer can read or modify another customer's records | | Secrets handling | No API keys in frontend code, logs, or public repos | Prevents credential theft and billing abuse | Attackers call third-party APIs on your dime | | Input validation | All onboarding inputs are validated server-side | Blocks injection and malformed payloads | Broken forms, bad records, exploit paths | | Rate limiting | Sensitive routes have rate limits and abuse controls | Reduces brute force and signup spam | Bot signups, password attacks, support overload | | Email authentication | SPF, DKIM, and DMARC all pass | Improves inbox placement for onboarding mail | Verification emails land in spam or fail completely | | TLS and redirects | HTTPS enforced with canonical redirects | Protects sessions and SEO trust signals | Mixed content warnings and insecure logins | | Tenant isolation | Queries always filter by tenant/workspace ID | Prevents data leakage in marketplace products | Cross-tenant access incidents | | Observability | Errors, auth failures, and webhook failures are logged safely | Lets you detect issues before users churn | Silent failures during onboarding | | Performance baseline | p95 core API under 500 ms; LCP under 2.5 s on key pages | Keeps signup conversion stable | Slow onboarding causes drop-off and ad waste |

The Checks I Would Run First

1. Tenant isolation on every onboarding endpoint

Signal: I look for any endpoint that fetches user data without an explicit tenant filter. In marketplace SaaS apps, this is where one customer's workspace can accidentally see another customer's records.

Tool or method: I review the route handlers, ORM queries, RLS policies if you use Postgres, and test cases with two seeded tenants. I also try manual ID swapping in requests to see if the API returns data from the wrong account.

Fix path: I add tenant scoping at the database query level first, not only in UI code. If you are using Supabase or Postgres RLS, I enforce policies there too. This is one of the highest-risk issues because it becomes a breach even when the frontend looks fine.

2. Auth bypasses on signup, invite acceptance, and password reset

Signal: I test whether protected routes can be reached with expired tokens, missing tokens, reused magic links, or manipulated invite URLs. Onboarding flows often get rushed here because founders focus on UX instead of access control.

Tool or method: I use browser dev tools plus a simple request replay tool like Postman or curl to tamper with session cookies and bearer tokens. I also check whether token expiry is enforced server-side.

Fix path: I centralize auth middleware and make every protected route fail closed. If reset links or invites are used once only, I mark them as single-use server-side. If this fails today, do not launch customer onboarding yet.

3. Secrets exposure in frontend bundles and logs

Signal: I inspect built assets for API keys, private URLs, webhook secrets, service tokens, and environment variables that should never ship to the browser. AI-built apps often leak secrets because they were copied into client-side config during rapid prototyping.

Tool or method: I grep build output and source maps for obvious patterns like `sk_`, `pk_`, `secret`, `token`, `webhook`, `private`, then scan logs for accidental dumps. I also check Git history if the repo was shared with multiple tools.

Fix path: Move all sensitive calls behind server endpoints or edge functions. Rotate any exposed keys immediately. If you have already deployed leaked credentials once publicly accessible even briefly means treat them as compromised.

4. Email deliverability for verification and onboarding

Signal: I verify SPF/DKIM/DMARC alignment plus real inbox placement for verification emails. Marketplace products depend on email working because users need to confirm accounts before they can transact.

Tool or method: I check DNS records directly with your provider dashboard and use a seed inbox test across Gmail and Outlook. I also inspect bounce logs if available.

Fix path: Set SPF to authorize only your sending provider. Enable DKIM signing at the provider level. Start DMARC at `p=none` while monitoring reports if you are unsure about alignment.

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; adkim=s; aspf=s

This snippet is not fancy. It is useful because it gives you visibility before you enforce quarantine or reject policies.

5. Abuse controls on login, signup, password reset, and webhook endpoints

Signal: If someone can hammer your login form hundreds of times per minute without friction or blocking, your app is open to brute force attempts and bot noise. The same applies to password reset requests and public webhook receivers.

Tool or method: I simulate repeated requests from one IP address and from distributed requests across several IPs where possible. Then I inspect whether rate limits exist at the app layer and edge layer.

Fix path: Add rate limits on sensitive routes using Cloudflare WAF rules plus application-level throttling where needed. Use CAPTCHA only where abuse is visible; do not use it as a substitute for proper server controls.

6. Monitoring for failed auth flows and deployment regressions

Signal: I want alerts for spikes in login failures, email send failures, payment webhooks failing if they affect onboarding access, and error rates above baseline. Without this you find out from angry customers first.

Tool or method: I check uptime monitoring plus application logs plus error tracking such as Sentry or Logtail-style tooling. Then I run one full end-to-end test after deployment to make sure redirects still work after DNS changes.

Fix path: Set alerts on availability plus specific business events like "verification email sent" and "onboarding completed." For launch day this matters more than vanity metrics because failed onboarding directly kills conversion.

Red Flags That Need a Senior Engineer

1. You have no idea where secrets live anymore because Lovable/Bolt/Cursor copied them into multiple places. 2. Your auth logic exists partly in the frontend because "it was faster." 3. Marketplace users can switch workspace IDs in URLs or request bodies. 4. You cannot explain how emails are authenticated beyond "we connected SendGrid." 5. You already saw one suspicious login spike but did nothing because there was no alerting.

If any two of those are true, DIY becomes expensive fast. The hidden cost is not just security risk; it is support hours lost to broken onboarding while your acquisition spend keeps running.

DIY Fixes You Can Do Today

1. Audit environment variables now.

• Remove any secret from `.env.local` that gets bundled into client code.
• Rotate anything that has already been committed to GitHub.

2. Turn on HTTPS everywhere.

• Force canonical redirects from `http` to `https`.
• Make sure subdomains like `app.` and `api.` resolve correctly behind Cloudflare.

3. Verify SPF/DKIM/DMARC today.

• Check your DNS panel.
• Send a test verification email to Gmail and Outlook before launch.

4. Add basic rate limiting.

• Start with login, signup, password reset request endpoints.
• Even simple per-IP throttling is better than nothing.

5. Test tenant switching manually.

• Create two test accounts.
• Try changing IDs in URLs or request payloads.
• If anything leaks across accounts stop launch work immediately.

Where Cyprian Takes Over

This is exactly where my Launch Ready sprint fits:

• Domain setup
• Email setup
• Cloudflare configuration
• SSL installation
• Deployment hardening
• Secret handling review
• Uptime monitoring
• Handover checklist

Here is how failures map to the sprint:

| Failure found in checklist | What I fix in Launch Ready | Typical timeline | |---|---|---| | Exposed secrets | Move secrets server-side + rotate compromised keys + clean env vars | Same day | | Broken DNS / subdomains / redirects | Configure domain routing + canonical redirects + subdomain mapping | Same day | | Weak TLS / mixed content / SSL errors | Install SSL + force HTTPS + validate browser trust chain | Same day | | Email deliverability issues | Set SPF/DKIM/DMARC + verify sender identity + test inbox placement | Within 24 hours | | No monitoring / silent failure risk | Add uptime checks + alerting + handover notes for common incidents | Within 24 hours | | Deployment instability after AI edits | Production deploy review + rollback path + smoke tests after release | Within 48 hours |

My recommendation is simple: if your product will accept real customers inside a marketplace workflow this week, do not treat security as a later cleanup task. Fix launch infrastructure first so the first paying users do not become your QA team.

References

• Roadmap.sh API Security Best Practices: https://roadmap.sh/api-security-best-practices
• Roadmap.sh Cyber Security: https://roadmap.sh/cyber-security
• Roadmap.sh QA: https://roadmap.sh/qa
• OWASP Top Ten: https://owasp.org/www-project-top-ten/
• Cloudflare Docs on 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.*