Filter array by its keys using an array of allowed keys

Question

The callback function in array_filter() only passes in the array's values, not the keys.

Scenario: If I have-

$my_array = array("foo" => 1, "hello" => "world");

$allowed = array("foo", "bar");

Expected output:

$my_array = array("foo" => 1);

How can I delete all keys in $my_array that are not in the $allowed array?