authentication in specific site collection

Hi, I have a default web application running and two site collections inside. I am trying to set different groups to authenticate to these site collections. There is only the option to setup groups in the web application level but not in the site collections.

I am talking about restricting authentication in the sites collections.

for example , web application hxxp://company.com and two sites collection  hxxp://company.com/sites/one andhxxp://company.com/sites/two

I would like to have a certain group of domain users to authenticate to the first site collection and another group to the second site collection. Then there is a way from site collection settings to give permissions to the content inside.

Thank you.