access_log to track failed logins

[AJ Weber]

I have a login page that redirects (actually appends the parameter 
"?error=true" to the URL and lets the user try again).

I was trying to re-define "access_log" with a full path and (for now) 
"combined" to a separate file in that location in hopes of tracking 
failed logins in a separate log.  Originally, I had a regex nested 
location for the error redirect, then I took it out and put it in its 
own location.  Nothing seems to work.

This doesn't seem to work at all.  An empty log gets created at startup, 
but nothing ever gets written there.  Is it because the access logging 
is already done by the time the location is determined?

How can I somehow log when someone accesses the "login" page with the 
"error=true" parameter on the URL?

Thanks,
AJ