Launch Ready API security Checklist for mobile app: Ready for first 100 users in bootstrapped SaaS?.

Launch Ready API security Checklist for mobile app: Ready for first 100 users in bootstrapped SaaS?

If I say a mobile app is "ready" for the first 100 users, I do not mean "the screens load." I mean a stranger can sign up, authenticate, hit your API, pay if needed, and keep using the product without exposing customer data, breaking onboarding, or flooding you with support messages.

For a bootstrapped SaaS, ready means this: zero exposed secrets, no critical auth bypasses, p95 API latency under 500ms on the main user flows, basic rate limiting in place, logs that help you debug without leaking personal data, and a deployment path you can trust at 2 am. If any of those are missing, you do not have a launch problem. You have a production risk problem.

This checklist is written for founders who built with Lovable, Bolt, Cursor, React Native, Flutter, or similar tools and now need the product safe enough to invite the first 100 users. If your goal is early traction, the bar is not perfection. The bar is "no obvious way to get hacked, blocked by app review, or buried in support tickets."

Quick Scorecard

| Check | Pass criteria | Why it matters | What breaks if it fails | |---|---|---|---| | Auth enforcement | Every protected endpoint rejects unauthenticated requests | Prevents free access to private data and actions | Data exposure, account takeover | | Authorization | Users only access their own records | Stops cross-account leaks | Customer trust loss, legal risk | | Secret handling | No secrets in repo or client app; env vars only | Prevents API key theft | Billing abuse, third-party compromise | | Rate limiting | Login and sensitive endpoints limited per IP/user | Reduces brute force and abuse | Credential stuffing, downtime | | Input validation | API rejects malformed and oversized payloads | Stops crashes and injection paths | Broken flows, data corruption | | CORS policy | Only allowed origins can call browser-facing APIs | Limits unwanted cross-site calls | Token leakage, unauthorized calls | | Logging hygiene | No passwords, tokens, or PII in logs | Keeps incidents from becoming breaches | Privacy issues, incident escalation | | Monitoring | Uptime alerts and error alerts are active | Lets you catch failures before users do | Silent outages, lost signups | | TLS and domain setup | SSL active on all domains and subdomains; redirects correct | Protects login and signup traffic | Browser warnings, app review issues | | Email auth | SPF, DKIM, DMARC passing for sending domain | Improves deliverability for verification emails | Signup emails land in spam |

A simple target I use for first-launch readiness: no critical auth bypasses found in manual testing, SPF/DKIM/DMARC all passing on the sending domain, and p95 API latency under 500ms for signup and core actions.

The Checks I Would Run First

1. I test every protected endpoint as an unauthenticated user

Signal: If I can call `/api/me`, `/api/billing`, `/api/projects`, or any write endpoint without a valid session or token and get real data back, that is a hard fail.

Tool or method: I use Postman or curl with no token at all. Then I repeat with an expired token and a token from another user.

Fix path: Add authentication middleware at the route level, not just in the UI. The frontend can hide buttons; the backend must enforce access.

2. I check object-level authorization on every record fetch

Signal: If changing an ID in the request returns another user's record, you have an IDOR issue. This is one of the most common launch-stage API security failures.

Tool or method: I compare responses for two test accounts and manually swap resource IDs in GET, PUT, PATCH, and DELETE calls.

Fix path: Scope every query by both resource ID and current user or tenant ID. Do not trust client-supplied ownership fields.

3. I inspect secret storage from repo to mobile build

Signal: Any API key inside source code, config files committed to GitHub, mobile bundles, or public environment files is exposed. If your app can be decompiled and still reveal keys that hit paid services directly from the client, that is a serious risk.

Tool or method: Search the repo for `sk_`, `pk_`, `secret`, `token`, `Bearer`, `.env`, Firebase config files at build time. Then inspect the compiled mobile bundle if needed.

Fix path: Move privileged calls behind your backend. Keep only public publishable keys on device when absolutely required.

## Good pattern
API_BASE_URL=https://api.yourapp.com
PUBLIC_STRIPE_KEY=pk_live_xxx
## Never store private keys in mobile code

4. I verify rate limits on login and expensive endpoints

Signal: If repeated login attempts are unlimited or search endpoints can be spammed until your bill spikes or your database slows down under load spikes from one IP.

Tool or method: Send repeated requests from one IP using a simple script or Postman runner. Watch response codes after threshold limits are reached.

Fix path: Add per-IP and per-user throttles on login, OTP resend, password reset, file upload initiation, and any endpoint that triggers third-party cost.

5. I validate CORS and origin rules

Signal: If your API allows `*` with credentials enabled or accepts requests from random origins while using cookies/tokens in browser contexts, that is too open.

Tool or method: Test from an unauthorized origin using browser dev tools or a small local HTML page that tries to call your API.

Fix path: Allow only known app domains and subdomains. Keep local dev separate from production rules so you do not ship a permissive wildcard by accident.

6. I check observability before launch day

Signal: If something fails in production but you cannot see request IDs, error rates per endpoint, uptime status, or recent deploy history within minutes.

Tool or method: Trigger a harmless test error in staging and confirm it appears in logs plus monitoring alerts. Check whether uptime checks hit both web and API endpoints.

Fix path: Add uptime monitoring for domain health plus synthetic checks for login/signup/API health. Make sure logs exclude secrets but include trace IDs so support can diagnose fast.

Red Flags That Need a Senior Engineer

1. You have multiple auth systems mixed together.

• Example: Firebase auth plus custom JWT plus session cookies.
• Risk: broken login states and hard-to-debug access bugs.
• This usually needs cleanup before launch.

2. Your mobile app talks directly to third-party services with private keys.

• Risk: anyone who extracts the app can reuse those keys.
• This becomes billing abuse very quickly once real users arrive.

3. You do not know which endpoints are public vs private.

• Risk: accidental exposure of admin actions.
• That is not a styling issue; it is a security boundary issue.

4. Your deployment process depends on manual steps.

• Risk: one missed env var breaks production after release.
• The first outage often comes from "I forgot to set one thing."

5. You have no alerting beyond "users will tell us."

• Risk: silent downtime during your first paid acquisition push.
• That wastes ad spend and damages trust fast.

If any two of those are true at once, I would stop DIYing this and get senior help before launch.

DIY Fixes You Can Do Today

1. Remove secrets from any file synced to GitHub.

• Rotate exposed keys immediately if they were ever committed.
• Assume anything committed may already be copied elsewhere.

2. Turn on basic rate limiting at the edge if your stack supports it.

• Start with login, password reset, OTP resend, invite links.
• Even simple limits reduce brute force noise fast.

3. Review every endpoint name against its permission level.

• Make a list of public routes versus authenticated routes.
• If you cannot explain why each route is public or private in one sentence each,

fix that before launch.

4. Set up SPF DKIM DMARC for your sending domain.

• This helps verification emails reach inboxes instead of spam.
• For bootstrapped SaaS onboarding this matters more than most founders expect.

5. Add uptime monitoring now.

• Monitor homepage plus API health plus auth flow if possible.
• A cheap alert beats discovering failure through angry users at midnight.

Where Cyprian Takes Over

I treat this as a production safety sprint rather than a redesign project.

Here is how checklist failures map to what I deliver:

| Checklist failure | Service deliverable | Timeline impact | |---|---|---| | Domain misconfigurations / bad redirects / broken subdomains | DNS setup + redirects + subdomain routing + Cloudflare config + SSL issuance | Same day start; usually fixed inside first 12 hours | | Exposed secrets / weak environment setup | Production deployment hardening + env var audit + secrets cleanup + handover checklist | First half of sprint | | Weak email deliverability | SPF/DKIM/DMARC setup for sending domain | Same day if DNS access exists | | No DDoS protection / poor caching / slow responses under load | Cloudflare caching + edge protection + cache rules review + basic performance tuning | Within 24 hours | | No monitoring / no alerting / no rollback clarity | Uptime monitoring + deployment verification + handover notes | Final phase before handoff |

My recommended path is simple:

• First 12 hours: audit domain status,

deployment settings, secrets, email authentication, and critical API exposure points.

• Next 24 hours:

fix DNS, SSL, redirects, Cloudflare, production deploy, caching, monitoring, then retest core flows.

• Final handover:

give you a checklist showing what was changed, what remains risky, where credentials live, how to rotate them, and what to watch during the first week of users.

If your goal is the first 100 users in bootstrapped SaaS, I care less about perfect architecture diagrams and more about whether signup works, email lands, the app stays up, and no one can read another user's data by changing an ID.

That flow is deliberate because launch failures usually happen in that order too: audit misses something, a fix breaks another flow, tests are skipped, deployment goes out half-configured, and monitoring catches it after users complain. I prefer to compress that risk into one controlled sprint instead of stretching it across weeks of founder guesswork.

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
• OWASP API Security Top 10: https://owasp.org/API-Security/
• Cloudflare SSL/TLS documentation: https://developers.cloudflare.com/ssl/
• Google Workspace email authentication guide (SPF/DKIM/DMARC): https://support.google.com/a/topic/2752442

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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.*