RBAC

Action.php

<?php

namespace Project\Permission;

class Action
{
    public const VIEW_SOMETHING   = 'view_something';
    public const DELETE_SOMETHING = 'delete_something';

    private $value;

    public function __construct(string $value)
    {
        $reflection = new \ReflectionClass($this);
        if (!in_array($value, $reflection->getConstants(), true) {
            throw new Exception('Invalid enum value');
        }

        $this->value = $value;
    }

    public function getValue(): string
    {
        return $this->value;
    }

    public function isEqualTo(Action $action): bool
    {
        return $this->value == $action->getValue();
    }
}

bootstrap.php

<?php

namespace Project;

$config = include '../config.file.php';

require_once __DIR__ . '/vendor/autoload.php';

try {
     $db = new PDO('mysql:host='.$config['dbhost'].';dbname='.$config['dbname'].';charset=utf8mb4', $config['dbusername'], $config['dbpass']);
     $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
     $db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
} catch(PDOException $ex) {
    echo $ex->getMessage();
}

Role.php

<?php

namespace Project\Entity;

class Role
{
    private $actions;

    public function __construct(Action ...$actions)
    {
        $this->actions = $actions;
    }

    public function isEntitledTo(Action $action): bool
    {
         foreach ($this->actions as $allowedAction) {
             if ($action->isEqualTo($allowedAction)) {
                 return true;
             }
         }

         return false;
    }
}

usage.php

<?php

require_once __DIR__ . '/bootstrap.php';

$userRepository = new \Project\Storage\UserRepository($db);

$user = $userRepository->getByUsername('TheUsername');

if ($u->isEntitledTo(new Action(Action::VIEW_SOMETHING))) {
    echo "You have permission to view somethin.<br />";
}

User.php

<?php

namespace Project\Entity;

class User
{
    private $id;

    private $name;

    private $roles;

    public function __construct(int $id, string $name, Role ...$roles)
    {
        $this->id    = $id;
        $this->name  = $name;
        $this->roles = $roles;
    }

    public function isEntitledTo(Action $action): bool
    {
         foreach ($this->roles as $role) {
             if ($role->isEntitledTo($action)) {
                 return true;
             }
         }

         return false;
    }
}

UserRepository.php

<?php

namespace Project\Storage;

use Project\Entity\User;

class UserRepository
{
    private $db;

    public function __construct(PDO $db) {
        $this->db = $db;
    }

    public function getByUsername(string $username)
    {
        $sql = '
            SELECT 
                rbac_user_roles.USERname,
                rbac_user_roles.role_id,
                rbac_roles.role_name, 
                rbac_permissions.permission_id, 
                rbac_permissions.permission_description
            FROM 
                authorized_users,
                rbac_user_roles,
                rbac_roles,
                rbac_role_permissions,
                rbac_permissions
            WHERE
                authorized_users.USERname = rbac_user_roles.USERname
            AND 
                rbac_user_roles.role_id = rbac_roles.role_id
            AND
                rbac_role_permissions.permission_id = rbac_permissions.permission_id
            AND 
                rbac_roles.role_id = rbac_role_permissions.role_id
            AND 
                authorized_users.USERname = :username
        ';
        
        $stmt = $this-db->prepare($sql);

        $stmt->execute([
            'username' => $username
        ]);

        // build the complete User object including roles etc
        return User(/* pass in the data to build the user entity*/);
    }
}

UserRepository::17

$stmt = ' should be $sql = '

And between lines UserRepository::40-UserRepository::42 you need to add:

$stmt = $this-db->prepare($sql);

Role::16-17 should be

         foreach ($this->actions as $allowedAction) {
             if ($action->isEqualTo($allowedAction)) {

User::13 should be:

    public function __construct(int $id, string $name, Role ...$roles)

To see it in action: https://3v4l.org/AuQBn