my %param;
foreach ( sort { $user_details{$a} cmp $user_details{$b} } keys %user_details ){
    #this next line will clobber $param{user_name} each time through. 
    #$param{user_name} = $user_details{$_};
    #do your stuff.

    print "the key is $_\n";
    print "the value is $user_details{$_}\n";
}