Is there a way that nginx can deliver a site if the connection comes from a specific user

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http://serverfault.com – I'm looking for a way to set a parameter in my browser or some sort of token that allows nginx to select the site that is going to serve. I wish to put the configuration in the nginx sites-enabled folder. Something like /etc/nginx/sites-enabled/example.com-construction <- The site regular people would get /etc/nginx/sites-enabled/example.com <- The site I'll get The second site only applies for connections comming from specific users (no more than 10) marked by a param in their browser. (HowTos)