What is a Callback URL used for in a Canvas App?

In a Canvas App, a Callback URL plays a crucial role during the authentication process. When a user attempts to log in using an external authentication method, the system requires a Callback URL to direct users back to the application once the authentication is successfully completed. This URL serves as a destination that the authentication service will redirect the user back to after they have validated their credentials.

By specifying this URL, the Canvas App ensures a seamless user experience since users can continue their journey promptly after logging in, without encountering additional steps or confusion. This mechanism is primarily designed to maintain security and efficiency in the authentication workflow.

The other options relate to different functionalities within a Canvas App. Fetching data from external databases does not specifically require a Callback URL, as this process typically involves API requests to retrieve the necessary information. Similarly, while specifying the URL for embedded pages and defining the server location for the application are important aspects of app configuration, they do not directly involve the role of the Callback URL in managing user authentication flow.