auth_request called multiple times for same single request

[garyc]

I had a look around for expected behavior during large http 1.x POST
requests, it looks like the standards suggest that browsers should monitor
for 413 responses and terminate the body transmission but they don't:

https://stackoverflow.com/questions/18367824/how-to-cancel-http-upload-from-data-events/18370751#18370751

Chrome and Firefox have issues 4+ years old on this, doesn't look likely
that they will be addressed any time soon.

I think a two stage approach may be better for our scenario, too bad, this
almost worked!

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,276512,276571#msg-276571