The array can only contain the specified keys, any keys not present will fail validation. By default, associative data has no restrictions on the key => values that can be present. For example: you have filters for a search box that are passed to SQL, only the specified keys should be allowed to be sent and not any value in the array of filters.

This rule is best used in conjunction with the array rule, though it can be used standalone.

use Somnambulist\Components\Validation\Factory;

$validation = $factory->validate
([
    'filters' => ['foo' => 'bar', 'baz' => 'example']
],
[
    'filters' => 'array|array_can_only_have_keys:foo,bar',
]);

$validation->passes(); // true if filters only has the keys in array_can_only_have_keys