diff --git a/modules/swagger-codegen/src/main/resources/php/README.mustache b/modules/swagger-codegen/src/main/resources/php/README.mustache
index eeff364b156..f130f944d67 100644
--- a/modules/swagger-codegen/src/main/resources/php/README.mustache
+++ b/modules/swagger-codegen/src/main/resources/php/README.mustache
@@ -68,22 +68,27 @@ Please follow the [installation procedure](#installation--usage) and then run th
 require_once(__DIR__ . '/vendor/autoload.php');
 {{#apiInfo}}{{#apis}}{{#-first}}{{#operations}}{{#operation}}{{#-first}}{{#hasAuthMethods}}{{#authMethods}}{{#isBasic}}
 // Configure HTTP basic authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setUsername('YOUR_USERNAME');
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setPassword('YOUR_PASSWORD');{{/isBasic}}{{#isApiKey}}
+    ->setUsername('YOUR_USERNAME')
+    ->setPassword('YOUR_PASSWORD');{{/isBasic}}{{#isApiKey}}
 // Configure API key authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKey('{{{keyParamName}}}', 'YOUR_API_KEY');
+$config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKey('{{{keyParamName}}}', 'YOUR_API_KEY');
 // Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
-// {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKeyPrefix('{{{keyParamName}}}', 'Bearer');{{/isApiKey}}{{#isOAuth}}
+// $config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKeyPrefix('{{{keyParamName}}}', 'Bearer');{{/isApiKey}}{{#isOAuth}}
 // Configure OAuth2 access token for authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');{{/isOAuth}}{{/authMethods}}
+$config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');{{/isOAuth}}{{/authMethods}}
 {{/hasAuthMethods}}
 
-$api_instance = new {{invokerPackage}}\Api\{{classname}}();
+$apiInstance = new {{invokerPackage}}\Api\{{classname}}(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(){{#hasAuthMethods}},
+    $config{{/hasAuthMethods}}
+);
 {{#allParams}}${{paramName}} = {{{example}}}; // {{{dataType}}} | {{{description}}}
 {{/allParams}}
 
 try {
-    {{#returnType}}$result = {{/returnType}}$api_instance->{{{operationId}}}({{#allParams}}${{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}});{{#returnType}}
+    {{#returnType}}$result = {{/returnType}}$apiInstance->{{{operationId}}}({{#allParams}}${{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}});{{#returnType}}
     print_r($result);{{/returnType}}
 } catch (Exception $e) {
     echo 'Exception when calling {{classname}}->{{operationId}}: ', $e->getMessage(), PHP_EOL;
diff --git a/modules/swagger-codegen/src/main/resources/php/api_doc.mustache b/modules/swagger-codegen/src/main/resources/php/api_doc.mustache
index 6d0ad8ebbb4..4118b83c30d 100644
--- a/modules/swagger-codegen/src/main/resources/php/api_doc.mustache
+++ b/modules/swagger-codegen/src/main/resources/php/api_doc.mustache
@@ -23,22 +23,29 @@ Method | HTTP request | Description
 require_once(__DIR__ . '/vendor/autoload.php');
 {{#hasAuthMethods}}{{#authMethods}}{{#isBasic}}
 // Configure HTTP basic authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setUsername('YOUR_USERNAME');
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setPassword('YOUR_PASSWORD');{{/isBasic}}{{#isApiKey}}
+$config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()
+              ->setUsername('YOUR_USERNAME')
+              ->setPassword('YOUR_PASSWORD');
+{{/isBasic}}{{#isApiKey}}
 // Configure API key authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKey('{{{keyParamName}}}', 'YOUR_API_KEY');
+$config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKey('{{{keyParamName}}}', 'YOUR_API_KEY');
 // Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
-// {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKeyPrefix('{{{keyParamName}}}', 'Bearer');{{/isApiKey}}{{#isOAuth}}
+// $config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setApiKeyPrefix('{{{keyParamName}}}', 'Bearer');{{/isApiKey}}{{#isOAuth}}
 // Configure OAuth2 access token for authorization: {{{name}}}
-{{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');{{/isOAuth}}{{/authMethods}}
+$config = {{{invokerPackage}}}\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');{{/isOAuth}}{{/authMethods}}
 {{/hasAuthMethods}}
 
-$api_instance = new {{invokerPackage}}\Api\{{classname}}(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new {{invokerPackage}}\Api\{{classname}}(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(){{#hasAuthMethods}},
+    $config{{/hasAuthMethods}}
+);
 {{#allParams}}${{paramName}} = {{{example}}}; // {{{dataType}}} | {{{description}}}
 {{/allParams}}
 
 try {
-    {{#returnType}}$result = {{/returnType}}$api_instance->{{{operationId}}}({{#allParams}}${{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}});{{#returnType}}
+    {{#returnType}}$result = {{/returnType}}$apiInstance->{{{operationId}}}({{#allParams}}${{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}});{{#returnType}}
     print_r($result);{{/returnType}}
 } catch (Exception $e) {
     echo 'Exception when calling {{classname}}->{{operationId}}: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore-security-test/php/SwaggerClient-php/README.md b/samples/client/petstore-security-test/php/SwaggerClient-php/README.md
index 3c73985e40c..1f5c98d4da7 100644
--- a/samples/client/petstore-security-test/php/SwaggerClient-php/README.md
+++ b/samples/client/petstore-security-test/php/SwaggerClient-php/README.md
@@ -56,11 +56,15 @@ Please follow the [installation procedure](#installation--usage) and then run th
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi();
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $test_code_inject____end____rn_n_r = "test_code_inject____end____rn_n_r_example"; // string | To test code injection *_/ ' \" =end -- \\r\\n \\n \\r
 
 try {
-    $api_instance->testCodeInjectEndRnNR($test_code_inject____end____rn_n_r);
+    $apiInstance->testCodeInjectEndRnNR($test_code_inject____end____rn_n_r);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testCodeInjectEndRnNR: ', $e->getMessage(), PHP_EOL;
 }
diff --git a/samples/client/petstore-security-test/php/SwaggerClient-php/docs/Api/FakeApi.md b/samples/client/petstore-security-test/php/SwaggerClient-php/docs/Api/FakeApi.md
index 445abaf0855..6b76f9e222c 100644
--- a/samples/client/petstore-security-test/php/SwaggerClient-php/docs/Api/FakeApi.md
+++ b/samples/client/petstore-security-test/php/SwaggerClient-php/docs/Api/FakeApi.md
@@ -17,11 +17,15 @@ To test code injection *_/ ' \" =end -- \\r\\n \\n \\r
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $test_code_inject____end____rn_n_r = "test_code_inject____end____rn_n_r_example"; // string | To test code injection *_/ ' \" =end -- \\r\\n \\n \\r
 
 try {
-    $api_instance->testCodeInjectEndRnNR($test_code_inject____end____rn_n_r);
+    $apiInstance->testCodeInjectEndRnNR($test_code_inject____end____rn_n_r);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testCodeInjectEndRnNR: ', $e->getMessage(), PHP_EOL;
 }
diff --git a/samples/client/petstore/php/SwaggerClient-php/README.md b/samples/client/petstore/php/SwaggerClient-php/README.md
index 087c3105f8d..112c5b8ab08 100644
--- a/samples/client/petstore/php/SwaggerClient-php/README.md
+++ b/samples/client/petstore/php/SwaggerClient-php/README.md
@@ -56,11 +56,15 @@ Please follow the [installation procedure](#installation--usage) and then run th
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\AnotherFakeApi();
+$apiInstance = new Swagger\Client\Api\AnotherFakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\Client(); // \Swagger\Client\Model\Client | client model
 
 try {
-    $result = $api_instance->testSpecialTags($body);
+    $result = $apiInstance->testSpecialTags($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling AnotherFakeApi->testSpecialTags: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/AnotherFakeApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/AnotherFakeApi.md
index 5b443618999..9eaff87384b 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/AnotherFakeApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/AnotherFakeApi.md
@@ -19,11 +19,15 @@ To test special tags
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\AnotherFakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\AnotherFakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\Client(); // \Swagger\Client\Model\Client | client model
 
 try {
-    $result = $api_instance->testSpecialTags($body);
+    $result = $apiInstance->testSpecialTags($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling AnotherFakeApi->testSpecialTags: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
index 5a5bd8c3bda..da5558c386f 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeApi.md
@@ -27,11 +27,15 @@ Test serialization of outer boolean types
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\OuterBoolean(); // \Swagger\Client\Model\OuterBoolean | Input boolean as post body
 
 try {
-    $result = $api_instance->fakeOuterBooleanSerialize($body);
+    $result = $apiInstance->fakeOuterBooleanSerialize($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->fakeOuterBooleanSerialize: ', $e->getMessage(), PHP_EOL;
@@ -72,11 +76,15 @@ Test serialization of object with outer number type
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\OuterComposite(); // \Swagger\Client\Model\OuterComposite | Input composite as post body
 
 try {
-    $result = $api_instance->fakeOuterCompositeSerialize($body);
+    $result = $apiInstance->fakeOuterCompositeSerialize($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->fakeOuterCompositeSerialize: ', $e->getMessage(), PHP_EOL;
@@ -117,11 +125,15 @@ Test serialization of outer number types
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\OuterNumber(); // \Swagger\Client\Model\OuterNumber | Input number as post body
 
 try {
-    $result = $api_instance->fakeOuterNumberSerialize($body);
+    $result = $apiInstance->fakeOuterNumberSerialize($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->fakeOuterNumberSerialize: ', $e->getMessage(), PHP_EOL;
@@ -162,11 +174,15 @@ Test serialization of outer string types
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\OuterString(); // \Swagger\Client\Model\OuterString | Input string as post body
 
 try {
-    $result = $api_instance->fakeOuterStringSerialize($body);
+    $result = $apiInstance->fakeOuterStringSerialize($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->fakeOuterStringSerialize: ', $e->getMessage(), PHP_EOL;
@@ -207,11 +223,15 @@ To test \"client\" model
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\Client(); // \Swagger\Client\Model\Client | client model
 
 try {
-    $result = $api_instance->testClientModel($body);
+    $result = $apiInstance->testClientModel($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testClientModel: ', $e->getMessage(), PHP_EOL;
@@ -253,10 +273,17 @@ Fake endpoint for testing various parameters 假端點 偽のエンドポイン
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure HTTP basic authorization: http_basic_test
-Swagger\Client\Configuration::getDefaultConfiguration()->setUsername('YOUR_USERNAME');
-Swagger\Client\Configuration::getDefaultConfiguration()->setPassword('YOUR_PASSWORD');
+$config = Swagger\Client\Configuration::getDefaultConfiguration()
+              ->setUsername('YOUR_USERNAME')
+              ->setPassword('YOUR_PASSWORD');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $number = 8.14; // float | None
 $double = 1.2; // double | None
 $pattern_without_delimiter = "pattern_without_delimiter_example"; // string | None
@@ -273,7 +300,7 @@ $password = "password_example"; // string | None
 $callback = "callback_example"; // string | None
 
 try {
-    $api_instance->testEndpointParameters($number, $double, $pattern_without_delimiter, $byte, $integer, $int32, $int64, $float, $string, $binary, $date, $date_time, $password, $callback);
+    $apiInstance->testEndpointParameters($number, $double, $pattern_without_delimiter, $byte, $integer, $int32, $int64, $float, $string, $binary, $date, $date_time, $password, $callback);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testEndpointParameters: ', $e->getMessage(), PHP_EOL;
 }
@@ -326,7 +353,11 @@ To test enum parameters
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $enum_form_string_array = array("enum_form_string_array_example"); // string[] | Form parameter enum test (string array)
 $enum_form_string = "-efg"; // string | Form parameter enum test (string)
 $enum_header_string_array = array("enum_header_string_array_example"); // string[] | Header parameter enum test (string array)
@@ -337,7 +368,7 @@ $enum_query_integer = 56; // int | Query parameter enum test (double)
 $enum_query_double = 1.2; // double | Query parameter enum test (double)
 
 try {
-    $api_instance->testEnumParameters($enum_form_string_array, $enum_form_string, $enum_header_string_array, $enum_header_string, $enum_query_string_array, $enum_query_string, $enum_query_integer, $enum_query_double);
+    $apiInstance->testEnumParameters($enum_form_string_array, $enum_form_string, $enum_header_string_array, $enum_header_string, $enum_query_string_array, $enum_query_string, $enum_query_integer, $enum_query_double);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testEnumParameters: ', $e->getMessage(), PHP_EOL;
 }
@@ -384,11 +415,15 @@ test inline additionalProperties
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $param = new \stdClass; // object | request body
 
 try {
-    $api_instance->testInlineAdditionalProperties($param);
+    $apiInstance->testInlineAdditionalProperties($param);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testInlineAdditionalProperties: ', $e->getMessage(), PHP_EOL;
 }
@@ -428,12 +463,16 @@ test json serialization of form data
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\FakeApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\FakeApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $param = "param_example"; // string | field1
 $param2 = "param2_example"; // string | field2
 
 try {
-    $api_instance->testJsonFormData($param, $param2);
+    $apiInstance->testJsonFormData($param, $param2);
 } catch (Exception $e) {
     echo 'Exception when calling FakeApi->testJsonFormData: ', $e->getMessage(), PHP_EOL;
 }
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeClassnameTags123Api.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeClassnameTags123Api.md
index 8f826708f0c..af8699f0961 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeClassnameTags123Api.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/FakeClassnameTags123Api.md
@@ -18,15 +18,20 @@ To test class name in snake case
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure API key authorization: api_key_query
-Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key_query', 'YOUR_API_KEY');
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key_query', 'YOUR_API_KEY');
 // Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
-// Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key_query', 'Bearer');
-
-$api_instance = new Swagger\Client\Api\FakeClassnameTags123Api(new \Http\Adapter\Guzzle6\Client());
+// $config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key_query', 'Bearer');
+
+$apiInstance = new Swagger\Client\Api\FakeClassnameTags123Api(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $body = new \Swagger\Client\Model\Client(); // \Swagger\Client\Model\Client | client model
 
 try {
-    $result = $api_instance->testClassname($body);
+    $result = $apiInstance->testClassname($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling FakeClassnameTags123Api->testClassname: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/PetApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/PetApi.md
index 2c5edb0414e..46e42007fac 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/PetApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/PetApi.md
@@ -27,13 +27,18 @@ Add a new pet to the store
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $body = new \Swagger\Client\Model\Pet(); // \Swagger\Client\Model\Pet | Pet object that needs to be added to the store
 
 try {
-    $api_instance->addPet($body);
+    $apiInstance->addPet($body);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->addPet: ', $e->getMessage(), PHP_EOL;
 }
@@ -74,14 +79,19 @@ Deletes a pet
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $pet_id = 789; // int | Pet id to delete
 $api_key = "api_key_example"; // string | 
 
 try {
-    $api_instance->deletePet($pet_id, $api_key);
+    $apiInstance->deletePet($pet_id, $api_key);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->deletePet: ', $e->getMessage(), PHP_EOL;
 }
@@ -123,13 +133,18 @@ Multiple status values can be provided with comma separated strings
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $status = array("status_example"); // string[] | Status values that need to be considered for filter
 
 try {
-    $result = $api_instance->findPetsByStatus($status);
+    $result = $apiInstance->findPetsByStatus($status);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->findPetsByStatus: ', $e->getMessage(), PHP_EOL;
@@ -171,13 +186,18 @@ Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $tags = array("tags_example"); // string[] | Tags to filter by
 
 try {
-    $result = $api_instance->findPetsByTags($tags);
+    $result = $apiInstance->findPetsByTags($tags);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->findPetsByTags: ', $e->getMessage(), PHP_EOL;
@@ -219,15 +239,20 @@ Returns a single pet
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure API key authorization: api_key
-Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key', 'YOUR_API_KEY');
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key', 'YOUR_API_KEY');
 // Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
-// Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key', 'Bearer');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+// $config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key', 'Bearer');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $pet_id = 789; // int | ID of pet to return
 
 try {
-    $result = $api_instance->getPetById($pet_id);
+    $result = $apiInstance->getPetById($pet_id);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->getPetById: ', $e->getMessage(), PHP_EOL;
@@ -269,13 +294,18 @@ Update an existing pet
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $body = new \Swagger\Client\Model\Pet(); // \Swagger\Client\Model\Pet | Pet object that needs to be added to the store
 
 try {
-    $api_instance->updatePet($body);
+    $apiInstance->updatePet($body);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->updatePet: ', $e->getMessage(), PHP_EOL;
 }
@@ -316,15 +346,20 @@ Updates a pet in the store with form data
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $pet_id = 789; // int | ID of pet that needs to be updated
 $name = "name_example"; // string | Updated name of the pet
 $status = "status_example"; // string | Updated status of the pet
 
 try {
-    $api_instance->updatePetWithForm($pet_id, $name, $status);
+    $apiInstance->updatePetWithForm($pet_id, $name, $status);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->updatePetWithForm: ', $e->getMessage(), PHP_EOL;
 }
@@ -367,15 +402,20 @@ uploads an image
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure OAuth2 access token for authorization: petstore_auth
-Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
-
-$api_instance = new Swagger\Client\Api\PetApi(new \Http\Adapter\Guzzle6\Client());
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');
+
+$apiInstance = new Swagger\Client\Api\PetApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 $pet_id = 789; // int | ID of pet to update
 $additional_metadata = "additional_metadata_example"; // string | Additional data to pass to server
 $file = "/path/to/file.txt"; // \SplFileObject | file to upload
 
 try {
-    $result = $api_instance->uploadFile($pet_id, $additional_metadata, $file);
+    $result = $apiInstance->uploadFile($pet_id, $additional_metadata, $file);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling PetApi->uploadFile: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/StoreApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/StoreApi.md
index 9daa65eba7b..87cec61aa7b 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/StoreApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/StoreApi.md
@@ -22,11 +22,15 @@ For valid response try integer IDs with value < 1000. Anything above 1000 or non
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\StoreApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\StoreApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $order_id = "order_id_example"; // string | ID of the order that needs to be deleted
 
 try {
-    $api_instance->deleteOrder($order_id);
+    $apiInstance->deleteOrder($order_id);
 } catch (Exception $e) {
     echo 'Exception when calling StoreApi->deleteOrder: ', $e->getMessage(), PHP_EOL;
 }
@@ -67,14 +71,19 @@ Returns a map of status codes to quantities
 require_once(__DIR__ . '/vendor/autoload.php');
 
 // Configure API key authorization: api_key
-Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key', 'YOUR_API_KEY');
+$config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('api_key', 'YOUR_API_KEY');
 // Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
-// Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key', 'Bearer');
+// $config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKeyPrefix('api_key', 'Bearer');
 
-$api_instance = new Swagger\Client\Api\StoreApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\StoreApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client(),
+    $config
+);
 
 try {
-    $result = $api_instance->getInventory();
+    $result = $apiInstance->getInventory();
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling StoreApi->getInventory: ', $e->getMessage(), PHP_EOL;
@@ -112,11 +121,15 @@ For valid response try integer IDs with value <= 5 or > 10. Other values will ge
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\StoreApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\StoreApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $order_id = 789; // int | ID of pet that needs to be fetched
 
 try {
-    $result = $api_instance->getOrderById($order_id);
+    $result = $apiInstance->getOrderById($order_id);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling StoreApi->getOrderById: ', $e->getMessage(), PHP_EOL;
@@ -157,11 +170,15 @@ Place an order for a pet
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\StoreApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\StoreApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\Order(); // \Swagger\Client\Model\Order | order placed for purchasing the pet
 
 try {
-    $result = $api_instance->placeOrder($body);
+    $result = $apiInstance->placeOrder($body);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling StoreApi->placeOrder: ', $e->getMessage(), PHP_EOL;
diff --git a/samples/client/petstore/php/SwaggerClient-php/docs/Api/UserApi.md b/samples/client/petstore/php/SwaggerClient-php/docs/Api/UserApi.md
index a1b3fdf3089..52b0a351904 100644
--- a/samples/client/petstore/php/SwaggerClient-php/docs/Api/UserApi.md
+++ b/samples/client/petstore/php/SwaggerClient-php/docs/Api/UserApi.md
@@ -26,11 +26,15 @@ This can only be done by the logged in user.
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = new \Swagger\Client\Model\User(); // \Swagger\Client\Model\User | Created user object
 
 try {
-    $api_instance->createUser($body);
+    $apiInstance->createUser($body);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->createUser: ', $e->getMessage(), PHP_EOL;
 }
@@ -70,11 +74,15 @@ Creates list of users with given input array
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = array(new \Swagger\Client\Model\User()); // \Swagger\Client\Model\User[] | List of user object
 
 try {
-    $api_instance->createUsersWithArrayInput($body);
+    $apiInstance->createUsersWithArrayInput($body);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->createUsersWithArrayInput: ', $e->getMessage(), PHP_EOL;
 }
@@ -114,11 +122,15 @@ Creates list of users with given input array
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $body = array(new \Swagger\Client\Model\User()); // \Swagger\Client\Model\User[] | List of user object
 
 try {
-    $api_instance->createUsersWithListInput($body);
+    $apiInstance->createUsersWithListInput($body);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->createUsersWithListInput: ', $e->getMessage(), PHP_EOL;
 }
@@ -158,11 +170,15 @@ This can only be done by the logged in user.
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $username = "username_example"; // string | The name that needs to be deleted
 
 try {
-    $api_instance->deleteUser($username);
+    $apiInstance->deleteUser($username);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->deleteUser: ', $e->getMessage(), PHP_EOL;
 }
@@ -202,11 +218,15 @@ Get user by user name
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $username = "username_example"; // string | The name that needs to be fetched. Use user1 for testing.
 
 try {
-    $result = $api_instance->getUserByName($username);
+    $result = $apiInstance->getUserByName($username);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->getUserByName: ', $e->getMessage(), PHP_EOL;
@@ -247,12 +267,16 @@ Logs user into the system
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $username = "username_example"; // string | The user name for login
 $password = "password_example"; // string | The password for login in clear text
 
 try {
-    $result = $api_instance->loginUser($username, $password);
+    $result = $apiInstance->loginUser($username, $password);
     print_r($result);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->loginUser: ', $e->getMessage(), PHP_EOL;
@@ -294,10 +318,14 @@ Logs out current logged in user session
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 
 try {
-    $api_instance->logoutUser();
+    $apiInstance->logoutUser();
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->logoutUser: ', $e->getMessage(), PHP_EOL;
 }
@@ -334,12 +362,16 @@ This can only be done by the logged in user.
 <?php
 require_once(__DIR__ . '/vendor/autoload.php');
 
-$api_instance = new Swagger\Client\Api\UserApi(new \Http\Adapter\Guzzle6\Client());
+$apiInstance = new Swagger\Client\Api\UserApi(
+    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
+    // This is optional, `GuzzleHttp\Client` will be used as default.
+    new GuzzleHttp\Client()
+);
 $username = "username_example"; // string | name that need to be deleted
 $body = new \Swagger\Client\Model\User(); // \Swagger\Client\Model\User | Updated user object
 
 try {
-    $api_instance->updateUser($username, $body);
+    $apiInstance->updateUser($username, $body);
 } catch (Exception $e) {
     echo 'Exception when calling UserApi->updateUser: ', $e->getMessage(), PHP_EOL;
 }