App Designer - iFrame
iFrame is an app view type which is used to render any dynamic content supplied by the developer inside the app. In the following sections, let's see how to configure an iFrame app in App Designer.
For security reasons, browsers will restrict cross origin HTTP requests initiated from within scripts. This is called Cross-Origin Resource Sharing (CORS), a mechanism that uses additional HTTP headers to tell a browser to let a web application running at one origin (domain) have permission to access selected resources from a server at a different origin.
Hence, you must define the domains from different origin that you intend to access within your application in the app server.
Refer the following pages: