Endless HTTP auth attempts without 5xx error? [was: Basic HTTP auth prompting too many times]

[E.B.]

by the way, i changed to nginx basic_auth and when I enter
wrong credentials, it allows me endless tries.  i'm was used
to apache gives a 5xx page after three bad tries.  i guess you
could refresh that and try again in apache too, but endless
tries without a error for nginx?  is there a way to change this?
 
 >  I have set up HTTP auth using the auth_pam module (although
>  I'm not sure that module is the problem - it might be nginx
>  problem).
>  
>  https://github.com/stogh/ngx_http_auth_pam_module/
>  
>  All works great for a while----
>  
>  After some time, browsers begin to prompt for authentication
>  over
>  and over again (I guess once for every image, stylesheet,
>  script, etc?).
>  Or maybe it is prompting because the credentials failed, but
>  I don't
>  think so because if I hit cancel/ESC over and over again, I
>  can use
>  the web page (I'm still authenticated), but none of the
>  images or
>  scripts have loaded.
>  
>  The logs don't show any indication of what caused the
>  prompts to
>  start showing. Previously, I saw this error (in nginx's
>  error log)
>  associated with the situation:
>  
>  Can't initialize threads: error 11
>  
>  This looks a little like a MySQL error (I use pam_mysql
>  behind
>  auth_pam).I don't know if there is some bad code in
>  auth_pam
>  causing this(?). Restarting nginx fixed the prompting in
>  this case.
>  
>  However, today, the prompting started again and the above
>  error
>  does NOT appear. I don't see any errors. Browser doesn't
>  matter -
>  tried it on firefox, mobile, whatever.
>  
>  I will try to test with just the built-in basic auth but
>  that's not a long
>  term solution for me, I need pam/mysql behind the auth (lot
>  of virt
>  users).