diff --git a/src/Entities/Interfaces/AccessTokenEntityInterface.php b/src/Entities/Interfaces/AccessTokenEntityInterface.php
index 242bc8da..2f62f045 100644
--- a/src/Entities/Interfaces/AccessTokenEntityInterface.php
+++ b/src/Entities/Interfaces/AccessTokenEntityInterface.php
@@ -4,4 +4,4 @@ namespace League\OAuth2\Server\Entities\Interfaces;
 interface AccessTokenEntityInterface extends TokenInterface
 {
 
-}
\ No newline at end of file
+}
diff --git a/src/Entities/ScopeEntity.php b/src/Entities/ScopeEntity.php
index 09fd0227..5c21e55e 100644
--- a/src/Entities/ScopeEntity.php
+++ b/src/Entities/ScopeEntity.php
@@ -15,7 +15,7 @@ class ScopeEntity implements ScopeEntityInterface
     /**
      * @inheritdoc
      */
-    function jsonSerialize()
+    public function jsonSerialize()
     {
         return $this->getIdentifier();
     }
diff --git a/src/Entities/Traits/ClientEntityTrait.php b/src/Entities/Traits/ClientEntityTrait.php
index fee28e0e..80e61b93 100644
--- a/src/Entities/Traits/ClientEntityTrait.php
+++ b/src/Entities/Traits/ClientEntityTrait.php
@@ -25,4 +25,4 @@ trait ClientEntityTrait
     {
         $this->name = $name;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Entities/Traits/RefreshTokenTrait.php b/src/Entities/Traits/RefreshTokenTrait.php
index 71e39225..0e0a3500 100644
--- a/src/Entities/Traits/RefreshTokenTrait.php
+++ b/src/Entities/Traits/RefreshTokenTrait.php
@@ -50,4 +50,4 @@ trait RefreshTokenTrait
     {
         $this->expiryDateTime = $dateTime;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Entities/Traits/TokenEntityTrait.php b/src/Entities/Traits/TokenEntityTrait.php
index d16e6f8d..324de912 100644
--- a/src/Entities/Traits/TokenEntityTrait.php
+++ b/src/Entities/Traits/TokenEntityTrait.php
@@ -123,4 +123,4 @@ trait TokenEntityTrait
     {
         return (new DateTime()) > $this->getExpiryDateTime();
     }
-}
\ No newline at end of file
+}
diff --git a/src/Exception/OAuthServerException.php b/src/Exception/OAuthServerException.php
index 09ef4ec5..35c38dd2 100644
--- a/src/Exception/OAuthServerException.php
+++ b/src/Exception/OAuthServerException.php
@@ -60,7 +60,8 @@ class OAuthServerException extends \Exception
         $localizedHint = null
     ) {
         $errorMessage = (is_null($localizedError))
-            ? 'The provided authorization grant is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client.'
+            ? 'The provided authorization grant is invalid, expired, revoked, does not match ' .
+                'the redirection URI used in the authorization request, or was issued to another client.'
             : $localizedError;
         $hint = (is_null($localizedHint))
             ? 'Check the `grant_type` parameter'
@@ -106,7 +107,8 @@ class OAuthServerException extends \Exception
         $localizedHint = null
     ) {
         $errorMessage = (is_null($localizedError))
-            ? 'The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed.'
+            ? 'The request is missing a required parameter, includes an invalid parameter value, ' .
+                'includes a parameter more than once, or is otherwise malformed.'
             : $localizedError;
         $hint = (is_null($localizedHint))
             ? sprintf('Check the `%s` parameter', $parameter)
diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index c6ffc760..01917c91 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -11,6 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use League\Event\EmitterAwareTrait;
 use League\Event\EmitterInterface;
 use League\Event\Event;
 use League\OAuth2\Server\Entities\AccessTokenEntity;
@@ -29,6 +30,8 @@ use Psr\Http\Message\ServerRequestInterface;
  */
 abstract class AbstractGrant implements GrantTypeInterface
 {
+    use EmitterAwareTrait;
+
     const SCOPE_DELIMITER_STRING = ' ';
 
     /**
@@ -60,11 +63,6 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected $accessTokenRepository;
 
-    /**
-     * @var \League\Event\Emitter
-     */
-    protected $emitter;
-
     /**
      * @var ScopeRepositoryInterface
      */
@@ -128,7 +126,7 @@ abstract class AbstractGrant implements GrantTypeInterface
     /**
      * @inheritdoc
      */
-    public function setEmitter(EmitterInterface $emitter)
+    public function setEmitter(EmitterInterface $emitter = null)
     {
         $this->emitter = $emitter;
     }
@@ -185,14 +183,14 @@ abstract class AbstractGrant implements GrantTypeInterface
         }
 
         $client = $this->clientRepository->getClientEntity(
+            $this->getIdentifier(),
             $clientId,
             $clientSecret,
-            null,
-            $this->getIdentifier()
+            null
         );
 
         if (!$client instanceof ClientEntityInterface) {
-            $this->emitter->emit(new Event('client.authentication.failed', $request));
+            $this->getEmitter()->emit(new Event('client.authentication.failed', $request));
 
             throw OAuthServerException::invalidClient();
         }
diff --git a/src/Grant/GrantTypeInterface.php b/src/Grant/GrantTypeInterface.php
index a6a5c63a..ece1d752 100644
--- a/src/Grant/GrantTypeInterface.php
+++ b/src/Grant/GrantTypeInterface.php
@@ -11,7 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
-use League\Event\EmitterInterface;
+use League\Event\EmitterAwareInterface;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
 use League\OAuth2\Server\Repositories\ClientRepositoryInterface;
 use League\OAuth2\Server\Repositories\ScopeRepositoryInterface;
@@ -21,7 +21,7 @@ use Psr\Http\Message\ServerRequestInterface;
 /**
  * Grant type interface
  */
-interface GrantTypeInterface
+interface GrantTypeInterface extends EmitterAwareInterface
 {
     /**
      * Set refresh token TTL
@@ -73,13 +73,6 @@ interface GrantTypeInterface
      */
     public function canRespondToRequest(ServerRequestInterface $request);
 
-    /**
-     * Set the event emitter
-     *
-     * @param \League\Event\EmitterInterface $emitter
-     */
-    public function setEmitter(EmitterInterface $emitter);
-
     /**
      * Set the client repository
      *
diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index 9f4f41e8..852dedb2 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -102,7 +102,7 @@ class PasswordGrant extends AbstractGrant
 
         $user = $this->userRepository->getUserEntityByUserCredentials($username, $password);
         if (!$user instanceof UserEntityInterface) {
-            $this->emitter->emit(new Event('user.authentication.failed', $request));
+            $this->getEmitter()->emit(new Event('user.authentication.failed', $request));
 
             throw OAuthServerException::invalidCredentials();
         }
diff --git a/src/Grant/RefreshTokenGrant.php b/src/Grant/RefreshTokenGrant.php
index cf3286c8..d5c7e854 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -38,9 +38,8 @@ class RefreshTokenGrant extends AbstractGrant
     /**
      * @param \League\OAuth2\Server\Repositories\RefreshTokenRepositoryInterface $refreshTokenRepository
      */
-    public function __construct(
-        RefreshTokenRepositoryInterface $refreshTokenRepository
-    ) {
+    public function __construct(RefreshTokenRepositoryInterface $refreshTokenRepository)
+    {
         $this->refreshTokenRepository = $refreshTokenRepository;
 
         $this->refreshTokenTTL = new \DateInterval('P1M');
@@ -67,7 +66,7 @@ class RefreshTokenGrant extends AbstractGrant
             // the request doesn't include any new scopes
             foreach ($scopes as $scope) {
                 if (in_array($scope->getIdentifier(), $oldRefreshToken['scopes']) === false) {
-                    $this->emitter->emit(new Event('scope.selection.failed', $request));
+                    $this->getEmitter()->emit(new Event('scope.selection.failed', $request));
 
                     throw OAuthServerException::invalidScope($scope->getIdentifier());
                 }
@@ -115,7 +114,7 @@ class RefreshTokenGrant extends AbstractGrant
 
         $refreshTokenData = json_decode($refreshToken, true);
         if ($refreshTokenData['client_id'] !== $clientId) {
-            $this->emitter->emit(new Event('refresh_token.client.failed', $request));
+            $this->getEmitter()->emit(new Event('refresh_token.client.failed', $request));
 
             throw OAuthServerException::invalidRefreshToken(
                 'Token is not linked to client,' .
diff --git a/src/Repositories/AuthCodeRepositoryInterface.php b/src/Repositories/AuthCodeRepositoryInterface.php
index 85852ef3..481106d3 100644
--- a/src/Repositories/AuthCodeRepositoryInterface.php
+++ b/src/Repositories/AuthCodeRepositoryInterface.php
@@ -33,8 +33,6 @@ interface AuthCodeRepositoryInterface extends RepositoryInterface
      * @param string  $code        The authorization code string
      * @param integer $expireTime  Token expire time
      * @param string  $redirectUri Client redirect uri
-     *
-     * @return void
      */
     public function persistNewAuthCode($code, $expireTime, $redirectUri);
 
diff --git a/src/Repositories/ClientRepositoryInterface.php b/src/Repositories/ClientRepositoryInterface.php
index b9b9aa3a..3bec9452 100644
--- a/src/Repositories/ClientRepositoryInterface.php
+++ b/src/Repositories/ClientRepositoryInterface.php
@@ -19,12 +19,12 @@ interface ClientRepositoryInterface extends RepositoryInterface
     /**
      * Get a client
      *
+     * @param string      $grantType        The grant type used
      * @param string      $clientIdentifier The client's identifier
      * @param string|null $clientSecret     The client's secret
      * @param string|null $redirectUri      The client's redirect URI
-     * @param string|null $grantType        The grant type used
      *
      * @return \League\OAuth2\Server\Entities\Interfaces\ClientEntityInterface
      */
-    public function getClientEntity($clientIdentifier, $grantType, $clientSecret = null, $redirectUri = null);
+    public function getClientEntity($grantType, $clientIdentifier, $clientSecret = null, $redirectUri = null);
 }
diff --git a/src/Repositories/MacTokenInterface.php b/src/Repositories/MacTokenInterface.php
index 4b84b147..833a0d7b 100644
--- a/src/Repositories/MacTokenInterface.php
+++ b/src/Repositories/MacTokenInterface.php
@@ -13,7 +13,6 @@ namespace League\OAuth2\Server\Storage;
 
 use League\OAuth2\Server\Repositories\RepositoryInterface;
 
-
 /**
  * MacTokenInterface
  */
@@ -21,15 +20,17 @@ interface MacTokenInterface extends RepositoryInterface
 {
     /**
      * Create a MAC key linked to an access token
-     * @param  string $macKey
-     * @param  string $accessToken
-     * @return void
+     *
+     * @param string $macKey
+     * @param string $accessToken
      */
     public function persistMacTokenEntity($macKey, $accessToken);
 
     /**
      * Get a MAC key by access token
+     *
      * @param  string $accessToken
+     *
      * @return string
      */
     public function getMacKeyByAccessTokenString($accessToken);
diff --git a/src/Repositories/RefreshTokenRepositoryInterface.php b/src/Repositories/RefreshTokenRepositoryInterface.php
index 1ac9a0d1..533351d8 100644
--- a/src/Repositories/RefreshTokenRepositoryInterface.php
+++ b/src/Repositories/RefreshTokenRepositoryInterface.php
@@ -21,9 +21,9 @@ interface RefreshTokenRepositoryInterface extends RepositoryInterface
     /**
      * Create a new refresh token_name
      *
-     * @param \League\OAuth2\Server\Entities\Interfaces\RefreshTokenEntityInterface $refreshTokenEntityInterface
+     * @param \League\OAuth2\Server\Entities\Interfaces\RefreshTokenEntityInterface $refreshTokenEntity
      */
-    public function persistNewRefreshToken(RefreshTokenEntityInterface $refreshTokenEntityInterface);
+    public function persistNewRefreshToken(RefreshTokenEntityInterface $refreshTokenEntity);
 
     /**
      * Revoke the refresh token
diff --git a/src/Repositories/ScopeRepositoryInterface.php b/src/Repositories/ScopeRepositoryInterface.php
index 276ce264..0b45efe9 100644
--- a/src/Repositories/ScopeRepositoryInterface.php
+++ b/src/Repositories/ScopeRepositoryInterface.php
@@ -19,9 +19,9 @@ interface ScopeRepositoryInterface extends RepositoryInterface
     /**
      * Return information about a scope
      *
-     * @param string $identifier The scope identifier
-     * @param string $grantType  The grant type used in the request
-     * @param string $clientId   The client sending the request
+     * @param string      $identifier The scope identifier
+     * @param string      $grantType  The grant type used in the request
+     * @param string|null $clientId   The client sending the request
      *
      * @return \League\OAuth2\Server\Entities\Interfaces\ScopeEntityInterface
      */
diff --git a/src/ResponseTypes/BearerTokenResponse.php b/src/ResponseTypes/BearerTokenResponse.php
index c67bc990..df30e94e 100644
--- a/src/ResponseTypes/BearerTokenResponse.php
+++ b/src/ResponseTypes/BearerTokenResponse.php
@@ -28,12 +28,14 @@ class BearerTokenResponse extends AbstractResponseType
      */
     public function generateHttpResponse(ResponseInterface $response)
     {
+        $expireDateTime = $this->accessToken->getExpiryDateTime()->getTimestamp();
+
         $jwtAccessToken = (new Builder())
             ->setAudience($this->accessToken->getClient()->getIdentifier())
             ->setId($this->accessToken->getIdentifier(), true)
             ->setIssuedAt(time())
             ->setNotBefore(time())
-            ->setExpiration($this->accessToken->getExpiryDateTime()->getTimestamp())
+            ->setExpiration($expireDateTime)
             ->setSubject($this->accessToken->getUserIdentifier())
             ->set('scopes', $this->accessToken->getScopes())
             ->sign(new Sha256(), new Key($this->pathToPrivateKey))
@@ -41,7 +43,7 @@ class BearerTokenResponse extends AbstractResponseType
 
         $responseParams = [
             'token_type'   => 'Bearer',
-            'expires_in'   => $this->accessToken->getExpiryDateTime()->getTimestamp() - (new \DateTime())->getTimestamp(),
+            'expires_in'   => $expireDateTime - (new \DateTime)->getTimestamp(),
             'access_token' => (string) $jwtAccessToken,
         ];
 
@@ -54,7 +56,7 @@ class BearerTokenResponse extends AbstractResponseType
                         'access_token_id'  => $this->accessToken->getIdentifier(),
                         'scopes'           => $this->accessToken->getScopes(),
                         'user_id'          => $this->accessToken->getUserIdentifier(),
-                        'expire_time'      => $this->refreshToken->getExpiryDateTime()->getTimestamp(),
+                        'expire_time'      => $expireDateTime,
                     ]
                 ),
                 $this->pathToPrivateKey
diff --git a/src/Server.php b/src/Server.php
index cc7eb320..b63ad6ed 100644
--- a/src/Server.php
+++ b/src/Server.php
@@ -2,7 +2,6 @@
 
 namespace League\OAuth2\Server;
 
-use DateInterval;
 use League\Event\EmitterAwareInterface;
 use League\Event\EmitterAwareTrait;
 use League\OAuth2\Server\Exception\OAuthServerException;