A user friendly, strong password generator PHP function.

strong-passwords.php

<?PHP
// Generates a strong password of N length containing at least one lower case letter,
// one uppercase letter, one digit, and one special character. The remaining characters
// in the password are chosen at random from those four sets.
//
// The available characters in each set are user friendly - there are no ambiguous
// characters such as i, l, 1, o, 0, etc. This, coupled with the $add_dashes option,
// makes it much easier for users to manually type or speak their passwords.
//
function generateStrongPassword($length = 9, $availableSets = 'luds'): string
{
    $sets = [
        'l' => 'abcdefghjkmnpqrstuvwxyz',
        'u' => 'ABCDEFGHJKMNPQRSTUVWXYZ',
        'd' => '23456789',
        's' => '!@#$%&*?',
    ];
    $availableSets = str_split($availableSets);
    $sets = array_filter($sets, fn($key) => in_array($key, $availableSets, true), ARRAY_FILTER_USE_KEY);

    $password = '';
    foreach ($sets as $set) {
        $password .= $set[random_int(0, strlen($set) - 1)];
    }

    $all = implode('', $sets);
    for ($i = 0; $i < $length - count($sets); $i++) {
        $password .= $all[random_int(0, strlen($all) - 1)];
    }

    return str_shuffle($password);
}