What is OAuth?
Also called OAuth 2.0, OAuth2.
OAuth is an open standard that lets an application act on a user's behalf inside another service without ever seeing that user's password. The user approves a limited scope of access at the service itself, and the application receives a token that grants only what was approved and can be revoked at any time. OAuth 2.0 is the version in general use.
In the usual flow the application redirects the user to the provider, the user signs in there and reviews the requested permissions, and the provider redirects back with a short lived code that the application exchanges for an access token. A refresh token normally accompanies it so access can continue after the access token expires, without prompting the user again.
The alternative, collecting someone's credentials and using them directly, gives an application unlimited and unrevocable access while spreading passwords across systems. OAuth confines each grant to named scopes, makes every grant visible to the user in one place, and reduces revocation to a single action. That is why mainstream services use it for third party access.
The most common confusion is calling OAuth an authentication protocol. It authorizes access to resources, while proving who the user is requires the identity layer built on top of it. Other frequent errors are requesting far broader scopes than a feature needs, storing tokens without encryption, and mishandling expiry and revocation, which produces integrations that silently stop working.
For AI agents, OAuth is the mechanism that makes delegated action accountable. Tokens are issued per user and per scope, so an agent inherits exactly the permissions its user granted and nothing more. Remote tool servers increasingly define OAuth based authorization for this reason, and per user tokens are what make an audit trail meaningful after the fact.
Key points
- Delegated access without sharing the user's password.
- The user consents to named scopes at the provider, not the application.
- Short lived access tokens plus refresh tokens, both revocable.
- Authorization rather than authentication, which needs a layer on top.
- Request the narrowest scope the feature actually needs.
In practice
A scheduling assistant needs to read a user's calendar. It sends the user to their calendar provider, where they sign in and see a request for read access to events and nothing more. They approve, the provider hands the assistant a token, and the assistant reads free and busy times. The assistant never learns the password, cannot send email, and loses access the moment the user revokes it.