Can you explain the difference between authentication and authorization for an app that uses third-party login?

Yes.

For an app that uses third-party login, the difference is:

• Authentication = Who are you?
• Authorization = What are you allowed to do?

Authentication

This happens when a user signs in with a third party like Google, Apple, or Facebook.

Example:

• “Log in with Google”
• Google verifies the person’s identity
• Your app trusts Google’s result and says: “This user is Alice”

So authentication is about confirming identity.

Authorization

This happens after the user is signed in.

Your app decides what that authenticated user can access or do.

Example:

• Alice can view her own profile
• Only admins can access the admin dashboard
• The app may ask for permission to read Google contacts or calendar

So authorization is about permissions and access rights.

Simple analogy

• Authentication = showing your ID at the door
• Authorization = getting a wristband that determines which rooms you can enter

In third-party login flows

Third-party login often uses:

• OAuth for authorization
• OpenID Connect (OIDC) for authentication

A common confusion is that OAuth alone is mainly for granting access to resources, while OIDC adds identity information for sign-in.

Example scenario

If you sign in with Google:

1. Google confirms your identity → authentication
2. Your app checks whether you’re a premium user or admin → authorization
3. If your app asks permission to access your Google Drive, that permission is also part of authorization

If you want, I can also show this with a real login flow diagram or explain OAuth vs OpenID Connect.