diff --git a/.gitignore b/.gitignore
index fa36fe5..7579f74 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,2 @@
 vendor
 composer.lock
-.idea
diff --git a/composer.json b/composer.json
index 06600fb..5e7386d 100644
--- a/composer.json
+++ b/composer.json
@@ -18,12 +18,14 @@
         }
     ],
     "require": {
-        "php": ">=5.4.0",
-        "behat/behat": "^3.0",
-        "guzzlehttp/guzzle": "^5.1"
+        "php": ">=7.0",
+        "behat/behat": "^3.3",
+        "guzzlehttp/guzzle": "^6.3",
+        "zendframework/zend-diactoros": "^1.4.1"
     },
     "autoload":{
-        "psr-4" : {"RstGroup\\Behat\\OAuth2\\Context\\": "src/"}
+        "psr-4" : {
+            "RstGroup\\Behat\\OAuth2\\Context\\": "src/"
+        }
     }
-
 }
diff --git a/features/password_grant_type.feature b/features/password_grant_type.feature
index 29e291f..1a8029e 100644
--- a/features/password_grant_type.feature
+++ b/features/password_grant_type.feature
@@ -17,7 +17,7 @@ Feature: OAuth2 Token Grant Password
         | username   | no       |
         | password   | bar      |
     And I send a access token request
-    Then the response status code is 400
+    Then the response status code is 401
     And the response has a "error" property and it is equals "invalid_grant"
     And the response has a "error_description" property
 
diff --git a/src/OAuth2Context.php b/src/OAuth2Context.php
index 3538570..70c9d73 100644
--- a/src/OAuth2Context.php
+++ b/src/OAuth2Context.php
@@ -1,18 +1,26 @@
 <?php
-/**
- * @licence http://opensource.org/licenses/MIT MIT
- */
+
+declare(strict_types=1);
 
 namespace RstGroup\Behat\OAuth2\Context;
 
-use Behat\Gherkin\Node\TableNode;
 use Behat\Behat\Context\SnippetAcceptingContext;
+use Behat\Gherkin\Node\TableNode;
+use Exception;
 use GuzzleHttp\Client as GuzzleHttpClient;
-use GuzzleHttp\Message\RequestInterface;
-use GuzzleHttp\Message\ResponseInterface;
+use GuzzleHttp\Psr7\Request;
+use LogicException;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+use Zend\Diactoros\Request\Serializer as RequestSerializer;
+use Zend\Diactoros\Response\Serializer as ResponseSerializer;
+use function GuzzleHttp\json_decode;
+use function GuzzleHttp\json_encode;
 
 /**
  * OAuth2 context for Behat BDD tool.
+ *
+ * @licence http://opensource.org/licenses/MIT MIT
  */
 class OAuth2Context implements SnippetAcceptingContext
 {
@@ -94,10 +102,10 @@ public function thatIHaveAnRefreshToken()
 
         $url = $this->parameters['token_url'];
         $response = $this->getPostResponseFromUrl($url, $parameters);
-        $data = json_decode($response->getBody(true), true);
+        $data = json_decode((string) $response->getBody(), true);
 
         if (!isset($data['refresh_token'])) {
-            throw new \Exception(sprintf("Error refresh token. Response: %s", $response->getBody(true)));
+            throw new Exception(sprintf("Error refresh token. Response: %s", (string) $response->getBody()));
         }
         $this->refreshToken = $data['refresh_token'];
     }
@@ -131,16 +139,16 @@ public function iMakeAAccessTokenRequest()
         $url = $this->parameters['token_url'];
         $this->response = $this->getPostResponseFromUrl($url, $this->requestBody);
 
-        $contentType = (string) $this->response->getHeader('Content-type');
+        $contentType = $this->response->getHeaderLine('Content-type');
 
         if ($contentType !== 'application/json') {
-            throw new \Exception(sprintf("Content-type must be application/json %s", $this->echoLastResponse()));
+            throw new Exception(sprintf("Content-type must be application/json %s", $this->echoLastResponse()));
         }
-        $this->data = json_decode($this->response->getBody(true));
+        $this->data = json_decode((string) $this->response->getBody());
         $this->lastErrorJson = json_last_error();
 
         if ($this->lastErrorJson != JSON_ERROR_NONE) {
-            throw new \Exception(sprintf("Error parsing response JSON " . "\n\n %s", $this->echoLastResponse()));
+            throw new Exception(sprintf("Error parsing response JSON " . "\n\n %s", $this->echoLastResponse()));
         }
     }
 
@@ -159,7 +167,7 @@ public function iMakeAAccessTokenRequestWithGivenRefreshToken()
     public function theResponseStatusCodeIs($httpStatus)
     {
         if ((string) $this->response->getStatusCode() !== $httpStatus) {
-            throw new \Exception(sprintf("HTTP code does not match %s (actual: %s)\n\n %s", $httpStatus, $this->response->getStatusCode(), $this->echoLastResponse()));
+            throw new Exception(sprintf("HTTP code does not match %s (actual: %s)\n\n %s", $httpStatus, $this->response->getStatusCode(), $this->echoLastResponse()));
         }
     }
 
@@ -177,8 +185,8 @@ public function theResponseHasAProperty($propertyName)
 
         try {
             return $this->getPropertyValue($propertyName);
-        } catch (\LogicException $e) {
-            throw new \Exception(sprintf("Property %s is not set!\n\n %s", $propertyName, $this->echoLastResponse()));
+        } catch (LogicException $e) {
+            throw new Exception(sprintf("Property %s is not set!\n\n %s", $propertyName, $this->echoLastResponse()));
         }
     }
 
@@ -204,7 +212,7 @@ public function theResponseHasAPropertyAndItsTypeIs($propertyName, $typeString)
                     break;
                 }
             default:
-                throw new \Exception(sprintf("Property %s is not of the correct type: %s!\n\n %s", $propertyName, $typeString, $this->echoLastResponse()));
+                throw new Exception(sprintf("Property %s is not of the correct type: %s!\n\n %s", $propertyName, $typeString, $this->echoLastResponse()));
         }
     }
 
@@ -218,7 +226,7 @@ public function theResponseHasAPropertyAndItIsEquals($propertyName, $propertyVal
         if ($value == $propertyValue) {
             return;
         }
-        throw new \Exception(sprintf("Given %s value is not %s\n\n %s", $propertyName, $propertyValue, $this->echoLastResponse()));
+        throw new Exception(sprintf("Given %s value is not %s\n\n %s", $propertyName, $propertyValue, $this->echoLastResponse()));
     }
 
     /**
@@ -226,7 +234,10 @@ public function theResponseHasAPropertyAndItIsEquals($propertyName, $propertyVal
      */
     public function echoLastResponse()
     {
-        $this->printDebug(sprintf("Request:\n %s \n\n Response:\n %s", $this->request, $this->response));
+        $request = RequestSerializer::toString($this->request);
+        $response = ResponseSerializer::toString($this->response);
+
+        $this->printDebug(sprintf("Request:\n %s \n\n Response:\n %s", $request, $response));
     }
 
     /**
@@ -240,21 +251,21 @@ public function theResponseHasTheOAuth2Format()
         ];
 
         foreach ($expectedHeaders as $name => $value) {
-            if ($this->response->getHeader($name) != $value) {
-                throw new \Exception(sprintf("Header %s is should be %s, %s given", $name, $value, $this->response->getHeader($name)));
+            $responseHeaderValue = $this->response->getHeaderLine($name);
+            if ($responseHeaderValue != $value) {
+                throw new Exception(sprintf("Header %s is should be %s, %s given", $name, $value, $responseHeaderValue));
             }
         }
     }
 
-    /**
-     * Get POST response from URL without ssl verify and exception propagation
-     *
-     * @param string $url POST URL
-     * @param array $body body array
-     */
-    protected function getPostResponseFromUrl($url, $body)
+    protected function getPostResponseFromUrl(string $url, array $body): ResponseInterface
     {
-        $this->request = $this->client->createRequest('POST', $url, ['body' => $body, 'verify' => false, 'exceptions' => false]);
+        $bodyAsQuery = http_build_query($body);
+        $headers = [
+            'Content-Type' => 'application/x-www-form-urlencoded',
+        ];
+        $this->request = new Request('POST', $url, $headers, $bodyAsQuery);
+
         return $this->client->send($this->request);
     }
 
@@ -263,7 +274,7 @@ protected function getPostResponseFromUrl($url, $body)
      *
      * @param string $propertyName property name
      */
-    protected function getPropertyValue($propertyName)
+    protected function getPropertyValue(string $propertyName)
     {
         return $this->getValue($propertyName, $this->data);
     }
@@ -274,10 +285,10 @@ protected function getPropertyValue($propertyName)
      * @param string $propertyName property name
      * @param mixed $data data as array or object
      */
-    protected function getValue($propertyName, $data)
+    protected function getValue(string $propertyName, $data)
     {
         if (empty($data)) {
-            throw new \Exception(sprintf("Response was not set %s", var_export($data, true)));
+            throw new Exception(sprintf("Response was not set %s", var_export($data, true)));
         }
         if (is_array($data) && array_key_exists($propertyName, $data)) {
             $data = $data[$propertyName];
@@ -287,7 +298,7 @@ protected function getValue($propertyName, $data)
             $data = $data->$propertyName;
             return $data;
         }
-        throw new \LogicException(sprintf("'%s' is not set", $propertyName));
+        throw new LogicException(sprintf("'%s' is not set", $propertyName));
     }
 
     /**
@@ -296,7 +307,7 @@ protected function getValue($propertyName, $data)
      * @param string $name header name
      * @param string $value value for header name
      */
-    protected function setHeader($name, $value)
+    protected function setHeader(string $name, string $value)
     {
         $this->headers[$name] = $value;
     }
@@ -313,7 +324,7 @@ protected function setHeaders(array $headers)
         }
     }
 
-    protected function getGuzzleParameters()
+    protected function getGuzzleParameters(): array
     {
         return isset($this->parameters[self::GUZZLE_PARAMETERS]) && is_array($this->parameters[self::GUZZLE_PARAMETERS]) ? $this->parameters[self::GUZZLE_PARAMETERS] : [];
     }
@@ -323,7 +334,7 @@ protected function getGuzzleParameters()
      *
      * @param string $string debug string
      */
-    public function printDebug($string)
+    public function printDebug(string $string)
     {
         echo sprintf("\n\033[36m| %s\033[0m\n\n", strtr($string, ["\n" => "\n|  "]));
     }