diff --git a/lib/Service/RegistrationService.php b/lib/Service/RegistrationService.php
index 49528d8..2dfd3b3 100644
--- a/lib/Service/RegistrationService.php
+++ b/lib/Service/RegistrationService.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2017 Julius Härtl <jus@bitgrid.net>
  * @copyright Copyright (c) 2017 Pellaeon Lin <pellaeon@hs.ntnu.edu.tw>
@@ -34,8 +37,6 @@ use OC\Authentication\Token\IToken;
 use OCA\Registration\Db\Registration;
 use OCA\Registration\Db\RegistrationMapper;
 use OCP\AppFramework\Db\DoesNotExistException;
-use \OCP\AppFramework\Http\TemplateResponse;
-use \OCP\AppFramework\Http\RedirectResponse;
 use OCP\ILogger;
 use OCP\IRequest;
 use OCP\ISession;
@@ -71,7 +72,7 @@ class RegistrationService {
 	/** @var ISecureRandom */
 	private $random;
 	/** @var IUserSession  */
-	private $usersession;
+	private $userSession;
 	/** @var IRequest */
 	private $request;
 	/** @var ILogger */
@@ -83,9 +84,23 @@ class RegistrationService {
 	/** @var ICrypto */
 	private $crypto;
 
-	public function __construct($appName, MailService $mailService, IL10N $l10n, IURLGenerator $urlGenerator,
-								RegistrationMapper $registrationMapper, IUserManager $userManager, IConfig $config, IGroupManager $groupManager,
-								ISecureRandom $random, IUserSession $us, IRequest $request, ILogger $logger, ISession $session, IProvider $tokenProvider, ICrypto $crypto) {
+	public function __construct(
+		string $appName,
+		MailService $mailService,
+		IL10N $l10n,
+		IURLGenerator $urlGenerator,
+		RegistrationMapper $registrationMapper,
+		IUserManager $userManager,
+		IConfig $config,
+		IGroupManager $groupManager,
+		ISecureRandom $random,
+		IUserSession $userSession,
+		IRequest $request,
+		ILogger $logger,
+		ISession $session,
+		IProvider $tokenProvider,
+		ICrypto $crypto
+	) {
 		$this->appName = $appName;
 		$this->mailService = $mailService;
 		$this->l10n = $l10n;
@@ -95,7 +110,7 @@ class RegistrationService {
 		$this->config = $config;
 		$this->groupManager = $groupManager;
 		$this->random = $random;
-		$this->usersession = $us;
+		$this->userSession = $userSession;
 		$this->request = $request;
 		$this->logger = $logger;
 		$this->session = $session;
@@ -103,21 +118,16 @@ class RegistrationService {
 		$this->crypto = $crypto;
 	}
 
-	/**
-	 * @param Registration $registration
-	 */
-	public function confirmEmail(Registration $registration) {
+	public function confirmEmail(Registration $registration): void {
 		$registration->setEmailConfirmed(true);
 		$this->registrationMapper->update($registration);
 	}
 
-	/**
-	 * @param Registration $registration
-	 */
-	public function generateNewToken(Registration $registration) {
+	public function generateNewToken(Registration $registration): void {
 		$this->registrationMapper->generateNewToken($registration);
 		$this->registrationMapper->update($registration);
 	}
+
 	/**
 	 * Create registration request, used by both the API and form
 	 * @param string $email
@@ -126,7 +136,7 @@ class RegistrationService {
 	 * @param string $displayname
 	 * @return Registration
 	 */
-	public function createRegistration($email, $username="", $password="", $displayname="") {
+	public function createRegistration(string $email, string $username = '', string $password = '', string $displayname = ''): Registration {
 		$registration = new Registration();
 		$registration->setEmail($email);
 		$registration->setUsername($username);
@@ -178,8 +188,8 @@ class RegistrationService {
 	 * @param string $displayname
 	 * @throws RegistrationException
 	 */
-	public function validateDisplayname($displayname) {
-		if ($displayname === "") {
+	public function validateDisplayname(string $displayname): void {
+		if ($displayname === '') {
 			throw new RegistrationException($this->l10n->t('Please provide a valid display name.'));
 		}
 	}
@@ -188,7 +198,7 @@ class RegistrationService {
 	 * @param string $username
 	 * @throws RegistrationException
 	 */
-	public function validateUsername($username) {
+	public function validateUsername(string $username): void {
 		if ($username === "") {
 			throw new RegistrationException($this->l10n->t('Please provide a valid user name.'));
 		}
@@ -204,7 +214,7 @@ class RegistrationService {
 	 * @param string $email
 	 * @return bool
 	 */
-	public function checkAllowedDomains($email) {
+	public function checkAllowedDomains(string $email): bool {
 		$allowed_domains = $this->config->getAppValue($this->appName, 'allowed_domains', '');
 		if ($allowed_domains !== '') {
 			$allowed_domains = explode(';', $allowed_domains);
@@ -223,9 +233,9 @@ class RegistrationService {
 	}
 
 	/**
-	 * @return array
+	 * @return string[]
 	 */
-	public function getAllowedDomains() {
+	public function getAllowedDomains(): array {
 		$allowed_domains = $this->config->getAppValue($this->appName, 'allowed_domains', '');
 		$allowed_domains = explode(';', $allowed_domains);
 		return $allowed_domains;
@@ -250,10 +260,10 @@ class RegistrationService {
 	 * @param $registration
 	 * @param string|null $username
 	 * @param string|null $password
-	 * @return \OCP\IUser
+	 * @return IUser
 	 * @throws RegistrationException|InvalidTokenException
 	 */
-	public function createAccount(Registration $registration, ?string $username = null, ?string $password = null) {
+	public function createAccount(Registration $registration, ?string $username = null, ?string $password = null): IUser {
 		if ($password === null && $registration->getPassword() === null) {
 			$generatedPassword = $this->generateRandomDeviceToken();
 			$registration->setPassword($this->crypto->encrypt($generatedPassword));
@@ -281,6 +291,7 @@ class RegistrationService {
 			throw new RegistrationException($this->l10n->t('Unable to create user, there are problems with the user backend.'));
 		}
 		$userId = $user->getUID();
+
 		// Set user email
 		try {
 			$user->setEMailAddress($registration->getEmail());
@@ -289,25 +300,25 @@ class RegistrationService {
 		}
 
 		// Add user to group
-		$registered_user_group = $this->config->getAppValue($this->appName, 'registered_user_group', 'none');
-		if ($registered_user_group !== 'none') {
-			$group = $this->groupManager->get($registered_user_group);
+		$registeredUserGroup = $this->config->getAppValue($this->appName, 'registered_user_group', 'none');
+		if ($registeredUserGroup !== 'none') {
+			$group = $this->groupManager->get($registeredUserGroup);
 			if ($group === null) {
 				// This might happen if $registered_user_group is deleted after setting the value
 				// Here I choose to log error instead of stopping the user to register
-				$this->logger->error("You specified newly registered users be added to '$registered_user_group' group, but it does not exist.");
+				$this->logger->error("You specified newly registered users be added to '$registeredUserGroup' group, but it does not exist.");
 				$groupId = '';
 			} else {
 				$group->addUser($user);
 				$groupId = $group->getGID();
 			}
 		} else {
-			$groupId = "";
+			$groupId = '';
 		}
 
 		// disable user if this is requested by config
-		$admin_approval_required = $this->config->getAppValue($this->appName, 'admin_approval_required', "no");
-		if ($admin_approval_required === "yes") {
+		$adminApprovalRequired = $this->config->getAppValue($this->appName, 'admin_approval_required', 'no');
+		if ($adminApprovalRequired === 'yes') {
 			$user->setEnabled(false);
 		}
 
@@ -353,19 +364,11 @@ class RegistrationService {
 		return $this->registrationMapper->findBySecret($secret);
 	}
 
-	/**
-	 * @param Registration $registation
-	 * @return null|\OCP\IUser
-	 */
-	public function getUserAccount(Registration $registation) {
-		$user = $this->userManager->get($registation->getUsername());
-		return $user;
+	public function getUserAccount(Registration $registration): ?IUser {
+		return $this->userManager->get($registration->getUsername());
 	}
 
-	/**
-	 * @param Registration $registration
-	 */
-	public function deleteRegistration(Registration $registration) {
+	public function deleteRegistration(Registration $registration): void {
 		$this->registrationMapper->delete($registration);
 	}
 
@@ -376,7 +379,7 @@ class RegistrationService {
 	 *
 	 * @return string
 	 */
-	private function generateRandomDeviceToken() {
+	private function generateRandomDeviceToken(): string {
 		$groups = [];
 		for ($i = 0; $i < 5; $i++) {
 			$groups[] = $this->random->generate(5, ISecureRandom::CHAR_HUMAN_READABLE);
@@ -389,7 +392,7 @@ class RegistrationService {
 	 * @return string
 	 * @throws RegistrationException
 	 */
-	public function generateAppPassword($uid) {
+	public function generateAppPassword(string $uid): string {
 		$name = $this->l10n->t('Registration app auto setup');
 		try {
 			$sessionId = $this->session->getId();
@@ -425,15 +428,15 @@ class RegistrationService {
 			$password = $this->crypto->decrypt($password);
 		}
 
-		$this->usersession->login($username, $password);
-		$this->usersession->createSessionToken($this->request, $userId, $username, $password);
+		$this->userSession->login($username, $password);
+		$this->userSession->createSessionToken($this->request, $userId, $username, $password);
 	}
 
 	/**
 	 * Replicates OC::cleanupLoginTokens() since it's protected
 	 * @param string $userId
 	 */
-	public function cleanupLoginTokens($userId) {
+	public function cleanupLoginTokens(string $userId): void {
 		$cutoff = time() - $this->config->getSystemValue('remember_login_cookie_lifetime', 60 * 60 * 24 * 15);
 		$tokens = $this->config->getUserKeys($userId, 'login_token');
 		foreach ($tokens as $token) {