Basic http auth with proxy pass showing 403/Forbidden

[strom]

Solution was stupid. I checked the error logs in nginx and found out
that my relative path was not where I expected it to be.

This works:
location ~ /(admin/.*|test) {
 auth_basic "Restricted";
 auth_basic_user_file htpasswd;
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,130796,130820#msg-130820