OAuth2 is the industry standard for delegated authorization, allowing users to grant third-party applications access to their data without sharing their credentials.
Let’s see how this plays out with a real-world example. Imagine a user wants to grant a "photo printing" app access to their Google Photos. Instead of giving the photo printing app their Google password (a massive security risk!), Google’s OAuth2 flow kicks in. The user is redirected to Google, logs in, and sees a prompt: "Allow Photo Printer App to access your photos?" If they approve, Google issues a temporary "access token" to the photo printing app. This token acts like a short-lived key, specifically granting permission to read photos, and nothing else. The app uses this token to fetch photos from Google Photos.
At its core, OAuth2 is about obtaining and using tokens. The flow typically involves:
- Authorization Request: The client application (e.g., the photo printing app) requests authorization from the resource owner (the user).
- Authorization Grant: The resource owner approves the request, and the authorization server (e.g., Google) grants an authorization grant (often a code).
- Token Request: The client application exchanges the authorization grant for an access token.
- Resource Access: The client application uses the access token to access protected resources (e.g., Google Photos API).
The "Bearer Token" part is a specific type of access token. When you have a bearer token, possession of the token is sufficient to gain access. Think of it like cash: whoever is holding the cash can spend it. There’s no additional verification needed by the resource server. This is why securing bearer tokens is paramount.
Here’s a simplified interaction in a Swagger/OpenAPI definition for JWT Bearer Authentication. This is how you’d document that an API expects a JWT as a bearer token in the Authorization header:
securitySchemes:
bearerAuth:
type: http
scheme: bearer
bearerFormat: JWT
description: JWT access token. Example: 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKK92w_d0n5eCjXv1j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9j_39x7x9