I built a fake Google login because my MVP demo could not wait for the OAuth console

I did not set out to build an identity product.

I set out to ship a thing with a login button, show it to someone, and get a reaction. You know the vibe: scaffold the app on a Saturday, wire up "Sign in with Google" because every boilerplate does, paste the env vars, run it once, record a Loom, send the link.

Then I spent the rest of the afternoon in the wrong console.

The demo was tomorrow. The product was not the blocker.

The UI was there. The callback route existed. My agent (or past me) had already dropped in Auth.js or whatever the stack wanted. On paper I was one env block away from done.

In practice I was:

• Creating OAuth clients in Google Cloud (again, because last time was another side project)


• Fighting redirect URI rules


• Doing the same dance for GitHub because the MVP had two buttons and looked "real"


• Re-reading docs about discovery URLs while the thing I actually cared about, onboarding, settings, the core loop, sat there mocking me

None of that was building my MVP. It was infrastructure tax I had to pay before I could even pretend to be a user in my own app.

If you are an MVP builder or a vibe coder, you have felt this. The energy is in the flow you want to show. The drag is in proving to a giant IdP that your localhost is allowed to exist.

What I actually needed

Not a better auth platform. Not enterprise SSO.

I needed to click login, land back in my app, see a name and email, and move on so I could:

• Test the post-login experience


• Demo to a friend, cofounder, or early user without saying "ignore auth for now"


• Iterate on redirect URLs and session handling without opening three vendor dashboards


• Feel like the MVP was real enough to judge, even when I had not earned production OAuth yet

That is a different job than "run authentication in production." It is make the social login path believable for dev, testing, and demos.

The moment I snapped

The breaking point was small and embarrassing.

I had a call in the morning. I wanted to show: sign in, land on dashboard, do the one thing my app does. The night before, Google OAuth started returning redirect_uri_mismatch because I had switched from port 3000 to 3001 after a template update. Fine. Fixable. But I was fixing their rules instead of my product.

I remember thinking: I am not blocked on product ideas. I am blocked on being a part-time admin for companies I do not work for yet.

So I did what a lot of us do when the tool we need does not exist. I hacked something local. Then I kept using it. Then it became dummyoauth.

Why I built dummyoauth (and what it is not)

dummyoauth is a mock OAuth/OIDC server for development and test. It stands in for Google, GitHub, Facebook, Microsoft, Cognito-shaped flows, and a plain OIDC profile, so your app talks to URLs that feel like the real providers while you are building.

I built it because I was tired of:

• Losing a whole evening to consoles when I only wanted to test "what happens after login"


• Treating every demo like a production launch checklist


• Having "we will hook up real auth later" mean my MVP never felt finished in anyone else's hands


• Maintaining separate mental models for "dev auth" vs "real auth" and shipping bugs when I finally switched

I did not build it to replace Clerk, Auth0, Cognito, or your production IdP. It is the stand-in you use while the MVP is still finding its shape.

The whole point is prototype with something that behaves like social login, then swap credentials when you are ready for the real apps. Same code path. Different env.

If this sounds like your week

You might be me if:

• You can ship UI in a day but social login steals the week


• Your demo script includes "pretend you're logged in" and you hate saying it


• You have three sign-in buttons and three consoles staring at you


• You are vibe-coding fast and keep getting slowed down by work that does not show up in the recording

I made dummyoauth for that person. Past me. Probably you.

Where it lives

• Try it out at: dummyoauth.com

If you are building an MVP right now, I am curious: what broke your last demo, redirects, test users, or just never getting around to the consoles? Reply and tell me. I have been there.