An in-browser proxy enables an application in a frame to make a cross domain request. The proxy executes within the browser, which has a first domain. The browser provides a frame in which a client application executes, which has a second domain. The request from the client application is a request for data access to the external domain. The proxy identifies a registration of the client application, and forwards the request to the external domain. The proxy receives a response to the request and provides the response back to the client application within the frame.