<serverUrl url="http://route.arcgis.com" matchAll="true"
And I've setup the log file for reporting on proxy connections. In the log file I see:
w3wp.exe Information: 0 : 2014-10-24 12:29:01 http://route.arcgis.com/arcgis/rest/services/World/Route/NAServer/Route_World/solve?f=json&returnDirections=true&returnRoutes=false&returnStops=false&returnBarriers=false&returnPolygonBarriers=false&returnPolylineBarriers=false&outSR=102100&directionsLengthUnits=esriNAUMiles&stops=%7B%22type%22%3A%22features%22%2C%22features%22%3A%5B%7B%22geometry%22%3A%7B%22x%22%3A%22-9811218.095255703%22%2C%22y%22%3A%225126606.098535776%22%2C%22spatialReference%22%3A%7B%22wkid%22%3A102100%2C%22latestWkid%22%3A3857%7D%7D%7D%2C%7B%22geometry%22%3A%7B%22x%22%3A-9812193.264436342%2C%22y%22%3A5128099.7029343285%2C%22spatialReference%22%3A%7B%22wkid%22%3A102100%2C%22latestWkid%22%3A3857%7D%7D%7D%5D%2C%22doNotLocateOnRestrictedElements%22%3Atrue%7D&callback=dojo.io.script.jsonp_dojoIoScript29._jsonpCallback
w3wp.exe Information: 0 : 2014-10-24 12:29:03 Matching credentials found in configuration file. OAuth 2.0 mode: True
w3wp.exe Information: 0 : 2014-10-24 12:29:03 Service is secured by https://www.arcgis.com/sharing/oauth2/: getting new token...
and then it stops. The browser calling it returns a runtime error. If I manually call the oauth2 page with the correct details from the server running the proxy then it works fine and returns a token okay.
Please could someone give me any advice on how I can further debug this?