Prevent your users to register with your route paths like login, or reserved usernames as their usernames in Laravel. More: https://blog.mahdyar.me/2021/04/18/route-paths-and-reserved-usernames-in-laravel/

AllowedUsername.php

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;
use Illuminate\Support\Facades\Route;

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

    /**
     * Determine if the validation rule passes.
     *
     * @param  string  $attribute
     * @param  string  $username
     * @return bool
     */
    public function passes($attribute, $username)
    {
        $username = trim(strtolower($username));

        if ($this->isReservedUsername($username)) {
            return false;
        }

        if ($this->matchesRoute($username)) {
            return false;
        }

        return true;
    }

    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message()
    {
        return 'The Username is reserved and cannot be registered.';
    }

    /**
     * Determine whether the given username is in the reserved usernames list.
     *
     * @param  string  $username
     * @return bool
     */
    private function isReservedUsername($username)
    {
        return in_array($username, config('auth.reserved_usernames'));
    }

    /**
     * Determine whether the given username matches an application route.
     *
     * @param  string  $username
     * @return bool
     */
    private function matchesRoute($username)
    {
        foreach (Route::getRoutes() as $route) {
            if (strtolower($route->uri) === $username) {
                return true;
            }
        }

        return false;
    }
}

auth.php

    /*
    |--------------------------------------------------------------------------
    | Reserved Usernames for Registration
    |--------------------------------------------------------------------------
    |
    | Here you may define the usernames that you don't want to be registered.
    | Note that routes are already excluded in "AllowedUsername" rule.
    |
    */

    'reserved_usernames' => [
        'admin', 
        'moderator',
    ],