If I want to use REST to get calendar information for lots of users, is there a way to do it without authenticating as each user first?

We'd like to be able to do:

$cal['username1'] = file_get_contents("http://zimbra/home/username1/calendar.html?view=day");
$cal['username2'] = file_get_contents("http://zimbra/home/username2/calendar.html?view=day");
$cal['username3'] = file_get_contents("http://zimbra/home/username3/calendar.html?view=day");

Is it possible to have our script log in as an admin user so all these URLs can be called without having to log in as each user?

Any advice much appreciated,