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Demystifying Desktop OAuth Understanding UUIDs, Session IDs ,and Secure Login Flows

3 min read

Introduction

During a deep dive into the OAuth implementation of a desktop application (e.g., Cursor), I encountered several identifiers like uuid, challenge, and authorization_session_id. These sparked critical questions about their purpose, security implications, and whether the system was susceptible to manipulation.

In this blog, I’ll walk through my questions, the answers I uncovered, and what they taught me about designing a secure desktop login system.

OAuth in Desktop Applications: A Quick Recap

Basic Flow:

  1. App requests login: It hits the auth server and receives a uuid and challenge.

  2. Redirect to browser: It opens a login page like:

    https://www.cursor.com/loginDeepControl?uuid=abc123&challenge=xyz456

  3. User logs in via OAuth (Google/GitHub).

  4. Auth server binds identity to uuid.

  5. App polls with uuid to complete login.

What Is uuid?

My question: Why do we need a uuid if the app already receives a session ID or challenge?

Answer:

  • uuid is a public identifier used by the desktop app.

  • It is safe to expose in URLs.

  • It helps correlate the app instance waiting for login.

This separation allows the server to keep internal identifiers private (authorization_session_id) and only expose what’s needed (uuid).

What Is authorization_session_id?

My question: What’s the difference between uuid and authorization_session_id?

Answer:

  • authorization_session_id is internal.

  • It tracks login state securely on the server.

  • Never shared with the desktop app.

Together, they offer separation of concerns: the client gets uuid, the server tracks state with authorization_session_id.

Why Is This Separation Useful?

This model improves security and architecture clarity:

  • The app can track login progress without access to sensitive session data.

  • If the server detects suspicious behavior, it can revoke or expire the session without revealing internal tokens.

How the System Prevents Exploits

A concern I raised was:

“If an attacker creates a login URL and tricks someone into authenticating, can’t they hijack the login?”

Yes — unless additional checks are in place.

Defenses:

  1. Confirmation UI:

    • Ask the user to confirm the app/device before finalizing login.

  2. Single-use UUIDs:

    • Make them expire in 60 seconds.

  3. Bind UUID to app metadata:

    • Tie to machine ID or IP address.

Final Thoughts

Key Takeaways:

  • uuid is a public-facing handle for login sessions.

  • authorization_session_id remains secure and internal.

  • Separation reduces leakage and allows secure polling.

  • Social engineering is still a risk if there’s no user confirmation.

What Developers Must Do:

  • Always validate the session request against user intent.

  • Avoid blindly trusting uuid-based logins.

  • Add feedback in the browser for who/what is logging in.

Conclusion

Understanding uuid and authorization_session_id helped me see how thoughtful design defends against subtle attacks. It also reminded me that protocol security isn’t enough — user awareness and session validation are just as vital.

Whether you’re a dev or a user, it pays to question what happens behind the scenes — and to design for the worst-case scenario.

Stay curious. Stay secure.

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