How can I define a Cordova inappbrowser proxy for Networks behind VPN and Proxy?

I am builing an Android Ionic2 App for my corporate network. The Network is accessed via OpenConnect or F5 VPN Tunnel before starting the app. The App uses the cordova InAppBrowser. All internal URLS can be accessed fine, but requests to any cdn in the open internet get a Timeout. So I need to define the corporate Proxy (fix or better proxy.pac) somewhere in the cordova/ionic environment. Any Ideas how? Thanks.