A strong password custom validation rule, based on Matt Kingshotts article: https://itnext.io/laravel-validation-rule-passwords-70364ae0f349

StrongPassword.php

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;

class StrongPassword implements Rule
{
    /**
     * Create a new rule instance.
     *
     * @return void
     */
    public function __construct()
    {
        //
    }

    /**
     * Determine if the validation rule passes.
     *
     * @param  string  $attribute
     * @param  mixed  $value
     * @return bool
     */
    public function passes($attribute, $value)
    {
        return preg_match(
            "/^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[#?!@()$%^&*=_{}[\]:;\"'|\\<>,.\/~`±§+-]).{12,30}$/", 
            $value
        );
    }

    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message()
    {
        return trans('validation.strong_password');
    }
}

Do not forget to add a language line to all the resources/lang/xx/validation.php files in your app. Like:

    'strong_password' => 
        'The :attribute must be 12–30 characters, and include a number, a symbol, a lower and a upper case letter',