Which OAuth flow is suitable for web applications with backend support?

The Web Server flow is the appropriate choice for web applications with backend support because it is designed to handle confidential client applications that can securely store client credentials. In this flow, the application directs the user's browser to an authorization server, where the user can log in and grant permission. Once granted, the authorization server redirects the user back to the application with an authorization code.

The key aspect of the Web Server flow is that the application can securely exchange the authorization code for an access token via a server-to-server request. This ensures that sensitive information, like client secrets and tokens, is not exposed to the user's browser, making it a secure option for web applications with backend components.

In contrast, other flows like the User-Agent flow and the Implicit flow are not suitable for backend support because they involve sending tokens directly to the user's browser, which can lead to security vulnerabilities. The Device flow is intended for devices that do not have a browser or a way to perform user interaction, which does not apply to standard web applications with backend support.