OAuth 2.0 Grant Types

OAuth 2.0 has become the de facto standard for managing access to user data and resources in modern applications. This protocol enables third-party applications to obtain limited access to a user’s resources on another service, such as Google or Facebook, without requiring the user to share their password. To achieve this, OAuth 2.0 utilizes a variety of “grant types” that cater to different scenarios and requirements. In this blog post, we’ll take a deep dive into the world of OAuth 2.0 grant types, exploring their purpose, benefits, and potential pitfalls.

Authorization Code Grant

The Authorization Code Grant is the most commonly used OAuth 2.0 grant type. It’s intended for applications that can securely maintain a client secret, such as web applications running on a server. The flow involves three parties: the user, the third-party application (client), and the resource server.

  • The user starts by accessing the client application and requesting access to their resources on the resource server.
  • The client application directs the user to the resource server’s authorization endpoint, where the user logs in and grants permission.
  • The resource server provides an authorization code, which the user returns to the client application.
  • The client application then exchanges the authorization code for an access token at the resource server’s token endpoint, using its client credentials (client ID and secret).

Implicit Grant

The Implicit Grant is designed for clients that cannot securely store a client secret, such as client-side JavaScript applications or mobile apps. This grant type simplifies the authorization process by directly providing an access token upon user authorization, eliminating the need for an authorization code exchange.

  • The user accesses the client application and requests access to their resources on the resource server.
  • The client application directs the user to the resource server’s authorization endpoint, where the user logs in and grants permission.
  • The resource server directly provides an access token, which the user returns to the client application.

Note that the Implicit Grant is considered less secure than the Authorization Code Grant, as the access token may be exposed in the user’s browser history or via URL sharing.

Resource Owner Password Credentials Grant

The Resource Owner Password Credentials Grant is intended for situations where the user has a high level of trust in the client application, such as first-party applications or internal tools. This grant type allows the client application to obtain an access token by directly collecting the user’s resource server credentials (username and password).

  • The user provides their resource server credentials to the client application.
  • The client application requests an access token from the resource server, including the user’s credentials and its own client credentials (client ID and secret).
  • This grant type should be used cautiously, as it requires the user to share their password with the client application, which can increase the risk of phishing or other attacks.

Client Credentials Grant

The Client Credentials Grant is designed for server-to-server communication, where the client application needs access to protected resources without user interaction. This grant type allows the client application to obtain an access token using only its client credentials (client ID and secret).

  • The client application requests an access token from the resource server, including its client credentials.
  • The resource server validates the credentials and issues an access token.