Caching authentication requests?

I want to use something like auth PAM but this seems to cause a PAM
conversation for every request and that is slower. Is there a way to
a successful authentication so that an authentication happens only once
every so many seconds?

I asked this question awhile ago but got no responses. I guess that
its either majorly stupid or completely obvious. I’m running on a
beaglebone and when I enable something like auth_pam the number of
I can handle drops from about 500 per second to about 30 which isn’t
suitable. Any kind of point would be help.

Posted at Nginx Forum: