<?php
	namespace Service\Auth;

	use Model\User;
	use Psr\Container\ContainerInterface;

	interface AuthInterface {
		/**
		 * @param \Psr\Container\ContainerInterface $container
		 */
		public function __construct(ContainerInterface $container);

		/**
		 * @return null|\Model\User
		 */
		public function user(): User;

		/**
		 * @return bool
		 */
		public function check(): bool;

		/**
		 * @return bool
		 */
		public function isAdmin(): bool;

		/**
		 * @param string $username
		 * @param string $password
		 * @param bool $rememberMe
		 *
		 * @return bool
		 */
		public function attempt(string $username, string $password, bool $rememberMe = false): bool;

		/**
		 * @return void
		 */
		public function logout(): void;
	}
?>

<?php
	namespace Service\Auth;

	use Model\User;
	use Psr\Container\ContainerInterface;

	interface AuthInterface {
		/**
		 * @param \Psr\Container\ContainerInterface $container
		 */
		public function __construct(ContainerInterface $container);

		/**
		 * @return null|\Model\User
		 */
		public function user(): ?User;

		/**
		 * @return bool
		 */
		public function check(): bool;

		/**
		 * @return bool
		 */
		public function isAdmin(): bool;

		/**
		 * @param string $username
		 * @param string $password
		 * @param bool $rememberMe
		 *
		 * @return bool
		 */
		public function attempt(string $username, string $password, bool $rememberMe = false): bool;

		/**
		 * @return void
		 */
		public function logout(): void;
	}
?>

Add missing return type nullable
Add missing return type nullable
