I built an auth backend for my own app — then tried selling it to see if it works

When I started working on a new mobile app recently (Android), I knew one thing for sure:

I didn’t want to rewrite authentication logic again.

Auth is one of those things you must get right, but it’s also the part I enjoy the least:
JWT setup, refresh tokens, expiry handling, logout, edge cases, and keeping libraries in sync.

I’ve worked with backends in my job before, but this time was different.

For this app, I decided to build the backend completely from scratch on my own — including auth — which I hadn’t owned end-to-end before. That alone made the project more interesting.

Instead of rushing through auth just to move on, I slowed down and treated it like a reusable backend.

I used:
Fastify
TypeScript
Prisma

And implemented:
JWT access tokens
Refresh tokens stored securely
Token rotation
Logout and revocation
Clean validation
A proper Postman setup to test flows

The goal was simple:
If I ever start another project, I should be able to reuse this without fear.

While doing this, a thought came up:

If I’m learning this the hard way, maybe other developers are too.

So I tried something small.
I cleaned the project, added proper environment configuration, removed generated files and secrets, and treated it like something that could be reused.

Then I asked myself a very honest question:

What if I try selling this — not to make money, but simply to see if anyone finds it useful?

No big expectations.
No launch hype.
Just curiosity.

A few things became clear very quickly:

Marketplaces don’t bring traffic automatically
Backend templates aren’t impulse buys
Selling dev tools is more about trust than features
Preparing something for others forces you to write cleaner code

And honestly, even if nobody buys it, the exercise itself was worth it.

I now have:
A solid auth base for my app
A backend I understand deeply because I built it myself
A clearer understanding of how developer products actually work

I’m sharing this not to aggressively sell anything, but because I see a lot of posts about passive income and overnight success, and very few about the real process.

The process where you:
Build something for the first time
Learn parts you avoided before
Are unsure about correctness
Put it out there anyway

If you’ve ever avoided auth because it felt risky, or built backend pieces without fully owning them, you’re not alone.

I documented what I built and shared it publicly for anyone curious.
The link is available on my profile.

Sometimes the goal isn’t immediate sales —
it’s learning whether an idea deserves more time.