diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 694e270..3279a01 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -64,7 +64,7 @@ public function __construct(
         }
     }
 
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         return 'authorization_code_oidc';
     }
@@ -72,7 +72,7 @@ public function getIdentifier()
     /**
      * {@inheritdoc}
      */
-    public function canRespondToAuthorizationRequest(ServerRequestInterface $request)
+    public function canRespondToAuthorizationRequest(ServerRequestInterface $request): bool
     {
         $result = parent::canRespondToAuthorizationRequest($request);
 
@@ -84,7 +84,7 @@ public function canRespondToAuthorizationRequest(ServerRequestInterface $request
         return $result;
     }
 
-    public function canRespondToAccessTokenRequest(ServerRequestInterface $request)
+    public function canRespondToAccessTokenRequest(ServerRequestInterface $request): bool
     {
         $requestParameters = (array) $request->getParsedBody();
 
@@ -112,7 +112,7 @@ public function canRespondToAccessTokenRequest(ServerRequestInterface $request)
     /**
      * {@inheritdoc}
      */
-    public function validateAuthorizationRequest(ServerRequestInterface $request)
+    public function validateAuthorizationRequest(ServerRequestInterface $request): AuthorizationRequest
     {
         $result = parent::validateAuthorizationRequest($request);
 
@@ -172,7 +172,7 @@ public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
         \DateInterval $accessTokenTTL
-    ) {
+    ): ResponseTypeInterface {
         /**
          * @var BearerTokenResponse $result
          */
@@ -238,7 +238,7 @@ protected function makeIdTokenInstance()
     /**
      * {@inheritdoc}
      */
-    public function completeAuthorizationRequest(AuthorizationRequest $authorizationRequest)
+    public function completeAuthorizationRequest(AuthorizationRequest $authorizationRequest): ResponseTypeInterface
     {
         if (!($authorizationRequest instanceof AuthenticationRequest)) {
             throw OAuthServerException::invalidRequest('not possible');
diff --git a/src/Grant/ImplicitGrant.php b/src/Grant/ImplicitGrant.php
index 9068342..d4c93ea 100644
--- a/src/Grant/ImplicitGrant.php
+++ b/src/Grant/ImplicitGrant.php
@@ -13,6 +13,7 @@
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
 use League\OAuth2\Server\RequestTypes\AuthorizationRequest;
 use League\OAuth2\Server\ResponseTypes\RedirectResponse;
+use League\OAuth2\Server\ResponseTypes\ResponseTypeInterface;
 use Psr\Http\Message\ServerRequestInterface;
 
 class ImplicitGrant extends \League\OAuth2\Server\Grant\ImplicitGrant
@@ -64,12 +65,12 @@ public function __construct(
         $this->queryDelimiter = $queryDelimiter;
     }
 
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         return 'implicit_oidc';
     }
 
-    public function canRespondToAuthorizationRequest(ServerRequestInterface $request)
+    public function canRespondToAuthorizationRequest(ServerRequestInterface $request): bool
     {
         $result = (isset($request->getQueryParams()['response_type'])
             && (
@@ -85,7 +86,7 @@ public function canRespondToAuthorizationRequest(ServerRequestInterface $request
         return $result && ($scopes && in_array('openid', explode(' ', $scopes)));
     }
 
-    public function validateAuthorizationRequest(ServerRequestInterface $request)
+    public function validateAuthorizationRequest(ServerRequestInterface $request): AuthorizationRequest
     {
         $result = parent::validateAuthorizationRequest($request);
 
@@ -142,7 +143,7 @@ public function validateAuthorizationRequest(ServerRequestInterface $request)
         return $result;
     }
 
-    public function completeAuthorizationRequest(AuthorizationRequest $authorizationRequest)
+    public function completeAuthorizationRequest(AuthorizationRequest $authorizationRequest): ResponseTypeInterface
     {
         if (!($authorizationRequest instanceof AuthenticationRequest)) {
             throw OAuthServerException::invalidRequest('not possible');
diff --git a/src/ResponseTypes/BearerTokenResponse.php b/src/ResponseTypes/BearerTokenResponse.php
index b296364..6f131fa 100644
--- a/src/ResponseTypes/BearerTokenResponse.php
+++ b/src/ResponseTypes/BearerTokenResponse.php
@@ -27,7 +27,7 @@ public function getAccessToken()
         return $this->accessToken;
     }
 
-    protected function getExtraParams(AccessTokenEntityInterface $accessToken)
+    protected function getExtraParams(AccessTokenEntityInterface $accessToken): array
     {
         /*
          The Claims requested by the profile, email, address, and phone scope values