You’ve set up OAuth. But are you actually secure?

I still remember the first time I implemented OAuth. It was during a late-night coding sprint. One of those “just get it working” kind of nights.

The goal was simple: allow users to log in with Google. And sure enough, after some copy-pasting and a few trial runs, it worked. Job done, right?

Well... not quite.

Back then, I didn’t fully understand the depth of OAuth as a protocol. Or how easy it is to misconfigure it in a way that attackers love. What seemed like a security upgrade was, in reality, a ticking time bomb.

Now, having observed quite a bit of OAuth integrations (and misconfigurations) at Beagle Security, I can confidently say this: OAuth misconfigurations are one of the most misunderstood yet common pitfalls in application security today.

What is OAuth (really)?

OAuth is not an authentication protocol. Let’s just get that out of the way.

OAuth 2.0 is a delegated authorization framework. It allows a third-party app to get limited access to a user’s resources on another service without exposing their credentials.

In plain terms:

“I want this app to access my Dropbox photos, but I’m not giving it my Dropbox password.”

That’s the beauty of OAuth. But it’s also where confusion begins.

Where things go wrong

Most developers don’t write OAuth flows from scratch. We rely on SDKs, plugins, and documentation snippets. And when something works, we tend to move on.

But OAuth has a lot of moving parts (redirect URIs, access tokens, scopes, client secrets) and if you don’t treat each of them carefully, you risk exposing users and systems to serious attacks.

Here are some of the most common missteps we see in the wild:

1. Overly permissive redirect URIs

OAuth requires you to register redirect URIs (where the OAuth provider sends users after login). But if you allow wildcards or fail to strictly validate them, attackers can hijack the flow.

Example:

nginx

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Redirect URI:

https://example.com/*

An attacker could use https://example.com/evil to intercept access tokens if your app doesn’t properly verify the full URI.

2. Storing secrets in public repos

This one still happens more than you’d expect. OAuth client IDs and secrets often end up hardcoded and committed to GitHub by mistake. Secrets aren’t secret once they’re public.

What to do:
Always use environment variables or secure vaults, and set up Git hooks or scanners to catch accidental leaks before they hit production.

3. Misunderstanding scopes

Scopes define what an app can access. But we often ask for more than we need, simply because it's easier or part of a copied example.

Over-requested scope example:

ini

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scope=email profile calendar.drive.readonly

Unless you really need all that data, you’re increasing risk — especially if an attacker gains control of a token.

4. Skipping state parameter validation

The state parameter is meant to prevent CSRF attacks during the OAuth flow. But many developers either skip it or don’t validate it properly.

When omitted or ignored, attackers can trick users into authorizing access to their accounts, then intercept the resulting token.

Fix:
Generate a secure, random state value for each OAuth request and verify it when handling the callback.

How to get OAuth right

Let’s shift gears and talk about what you can do to avoid these pitfalls:

Wrapping up

OAuth is powerful, but like most powerful things, it needs careful handling. Don’t treat it as a copy-paste task. Take the time to understand the flow, verify configurations, and test rigorously.

Because when something breaks, it won’t be the library or framework that gets blamed—it’ll be your brand.

You don’t just want OAuth working. You want it working securely.