OAuth 2.0 Device Flow Enables Secure Login on Smart TVs, CLIs, and Consoles

OAuth 2.0 Device Authorization Grant, known as Device Flow, solves the authentication challenge for devices like smart TVs, game consoles, and CLI tools that lack convenient input methods. Instead of logging in directly on the device, the user completes authentication on a separate phone or computer by visiting a verification URL and entering a short code. The original device receives a device code and user code from the authorization server, then repeatedly polls the token endpoint until the user finishes authenticating. Once the user approves access, the authorization server issues an access token that the original device uses to call protected APIs. The device must also handle intermediate responses such as authorization_pending, slow_down, expired_token, and access_denied to manage the polling process correctly.