$lines = file("secure.txt");
      print"$lines[0]";
      print "$lines[1]";
      if(    strcmp($_POST['username'],$lines[0]) == 0
          && strcmp($_POST['password'],$lines[1]) == 0)
      {
		//code
	}
	else
	{
		print access denied stuff
	}

secure.txt contains:
admin
password

user enters in the form
username: admin
password: password