how to get request user in sync function?

[atom992]

Hi, I want to log the modification of doc (I think it is important) , so I want to log request user in sync function,but I found I can not get request user from [userCtx.user]. I know that sync gateway must know the request user, and I can get the request user from HTTP log like this:

2015-07-24T01:51:44.887+08:00 HTTP:  #002: PUT /sync_test/DOC1  (as sguser)

but I want to log in JS log, so I can grep the log by JS to collection and analyze log.