HTTP request synchronization behind security proxies

[zbouziane]

Some actions need two http successive requests to be performed. Downloading a feed is an example of such an action. The first request download a token '/api/manager/${SecureOrPublic}/feedversion/${FeedVersion.id}/downloadtoken' then the second request uses this token to download the feed /api/manager/downloadfeed/${DownloadedToken}. The token is available for only one dowload, which causes the download of feeds fails for clients behind a security proxy that plays any http request twice. A first time to test the server and a second time to serve the original requester.