Prompt Title: OAuth2 Authorization Framework

OAuth2 is an authorization framework that allows a user to grant a third-party application access to their resources without revealing their credentials (such as a password). The framework is designed to provide secure authorization flows for web and mobile applications, as well as for API providers.

OAuth2 involves four parties: the resource owner (the user), the client (the third-party application), the authorization server (the server that authenticates the user and issues access tokens), and the resource server (the server that hosts the protected resources).

OAuth2 operates through a series of flows or grant types, each of which determines how the client obtains authorization to access the user's resources. The most common grant types are:

1. Authorization Code Grant: The client redirects the user to the authorization server to authenticate and authorize the client, and then the authorization server redirects the user back to the client with an authorization code. The client then exchanges the authorization code for an access token from the authorization server.

2. Implicit Grant: The client receives an access token directly from the authorization server after the user authenticates and authorizes the client.

3. Resource Owner Password Credentials Grant: The client directly obtains the user's credentials (username and password) and exchanges them for an access token from the authorization server.

4. Client Credentials Grant: The client uses its own credentials to obtain an access token from the authorization server, allowing it to access its own resources on behalf of the user.

OAuth2 is widely used by many popular websites and services, including Facebook, Google, and Twitter, to allow third-party applications to access user data without requiring users to share their login credentials.