diff --git a/src/php/composer.json b/src/php/composer.json
index 3c0cb37..ba7a130 100644
--- a/src/php/composer.json
+++ b/src/php/composer.json
@@ -5,7 +5,8 @@
   "homepage": "http://grpc.io",
   "license": "BSD-3-Clause",
   "require": {
-    "php": ">=5.5.0"
+    "php": ">=5.5.0",
+    "google/auth": "dev-master"
   },
   "autoload": {
     "psr-4": {
diff --git a/src/php/composer.lock b/src/php/composer.lock
index 47fc70f..c2d723d 100644
--- a/src/php/composer.lock
+++ b/src/php/composer.lock
@@ -4,12 +4,308 @@
         "Read more about it at http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "hash": "65467a098f5fd8b8fe5f7f6e10226f8a",
-    "packages": [],
+    "hash": "bb81ea5f72ddea2f594a172ff0f3b44d",
+    "packages": [
+        {
+            "name": "firebase/php-jwt",
+            "version": "2.0.0",
+            "target-dir": "Firebase/PHP-JWT",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/firebase/php-jwt.git",
+                "reference": "ffcfd888ce1e4f2d70cac2dc9b7301038332fe57"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/firebase/php-jwt/zipball/ffcfd888ce1e4f2d70cac2dc9b7301038332fe57",
+                "reference": "ffcfd888ce1e4f2d70cac2dc9b7301038332fe57",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.2.0"
+            },
+            "type": "library",
+            "autoload": {
+                "classmap": [
+                    "Authentication/",
+                    "Exceptions/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD-3-Clause"
+            ],
+            "authors": [
+                {
+                    "name": "Neuman Vong",
+                    "email": "neuman+pear@twilio.com",
+                    "role": "Developer"
+                },
+                {
+                    "name": "Anant Narayanan",
+                    "email": "anant@php.net",
+                    "role": "Developer"
+                }
+            ],
+            "description": "A simple library to encode and decode JSON Web Tokens (JWT) in PHP. Should conform to the current spec.",
+            "homepage": "https://github.com/firebase/php-jwt",
+            "time": "2015-04-01 18:46:38"
+        },
+        {
+            "name": "google/auth",
+            "version": "dev-master",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/google/google-auth-library-php.git",
+                "reference": "35f87159b327fa6416266948c1747c585a4ae3ad"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/google/google-auth-library-php/zipball/35f87159b327fa6416266948c1747c585a4ae3ad",
+                "reference": "35f87159b327fa6416266948c1747c585a4ae3ad",
+                "shasum": ""
+            },
+            "require": {
+                "firebase/php-jwt": "2.0.0",
+                "guzzlehttp/guzzle": "5.2.*",
+                "php": ">=5.4"
+            },
+            "require-dev": {
+                "phplint/phplint": "0.0.1",
+                "phpunit/phpunit": "3.7.*"
+            },
+            "type": "library",
+            "autoload": {
+                "classmap": [
+                    "src/"
+                ],
+                "psr-4": {
+                    "Google\\Auth\\": "src"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "Apache-2.0"
+            ],
+            "description": "Google Auth Library for PHP",
+            "homepage": "http://github.com/google/google-auth-library-php",
+            "keywords": [
+                "Authentication",
+                "google",
+                "oauth2"
+            ],
+            "time": "2015-04-30 11:57:19"
+        },
+        {
+            "name": "guzzlehttp/guzzle",
+            "version": "5.2.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/guzzle.git",
+                "reference": "475b29ccd411f2fa8a408e64576418728c032cfa"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/guzzle/zipball/475b29ccd411f2fa8a408e64576418728c032cfa",
+                "reference": "475b29ccd411f2fa8a408e64576418728c032cfa",
+                "shasum": ""
+            },
+            "require": {
+                "guzzlehttp/ringphp": "~1.0",
+                "php": ">=5.4.0"
+            },
+            "require-dev": {
+                "ext-curl": "*",
+                "phpunit/phpunit": "~4.0",
+                "psr/log": "~1.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "5.0-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "GuzzleHttp\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                }
+            ],
+            "description": "Guzzle is a PHP HTTP client library and framework for building RESTful web service clients",
+            "homepage": "http://guzzlephp.org/",
+            "keywords": [
+                "client",
+                "curl",
+                "framework",
+                "http",
+                "http client",
+                "rest",
+                "web service"
+            ],
+            "time": "2015-01-28 01:03:29"
+        },
+        {
+            "name": "guzzlehttp/ringphp",
+            "version": "1.0.7",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/RingPHP.git",
+                "reference": "52d868f13570a9a56e5fce6614e0ec75d0f13ac2"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/RingPHP/zipball/52d868f13570a9a56e5fce6614e0ec75d0f13ac2",
+                "reference": "52d868f13570a9a56e5fce6614e0ec75d0f13ac2",
+                "shasum": ""
+            },
+            "require": {
+                "guzzlehttp/streams": "~3.0",
+                "php": ">=5.4.0",
+                "react/promise": "~2.0"
+            },
+            "require-dev": {
+                "ext-curl": "*",
+                "phpunit/phpunit": "~4.0"
+            },
+            "suggest": {
+                "ext-curl": "Guzzle will use specific adapters if cURL is present"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "GuzzleHttp\\Ring\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                }
+            ],
+            "description": "Provides a simple API and specification that abstracts away the details of HTTP into a single PHP function.",
+            "time": "2015-03-30 01:43:20"
+        },
+        {
+            "name": "guzzlehttp/streams",
+            "version": "3.0.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/guzzle/streams.git",
+                "reference": "47aaa48e27dae43d39fc1cea0ccf0d84ac1a2ba5"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/guzzle/streams/zipball/47aaa48e27dae43d39fc1cea0ccf0d84ac1a2ba5",
+                "reference": "47aaa48e27dae43d39fc1cea0ccf0d84ac1a2ba5",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.4.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "~4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.0-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "GuzzleHttp\\Stream\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Michael Dowling",
+                    "email": "mtdowling@gmail.com",
+                    "homepage": "https://github.com/mtdowling"
+                }
+            ],
+            "description": "Provides a simple abstraction over streams of data",
+            "homepage": "http://guzzlephp.org/",
+            "keywords": [
+                "Guzzle",
+                "stream"
+            ],
+            "time": "2014-10-12 19:18:40"
+        },
+        {
+            "name": "react/promise",
+            "version": "v2.2.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/reactphp/promise.git",
+                "reference": "365fcee430dfa4ace1fbc75737ca60ceea7eeeef"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/reactphp/promise/zipball/365fcee430dfa4ace1fbc75737ca60ceea7eeeef",
+                "reference": "365fcee430dfa4ace1fbc75737ca60ceea7eeeef",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "2.0-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "React\\Promise\\": "src/"
+                },
+                "files": [
+                    "src/functions_include.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jan Sorgalla",
+                    "email": "jsorgalla@googlemail.com"
+                }
+            ],
+            "description": "A lightweight implementation of CommonJS Promises/A for PHP",
+            "time": "2014-12-30 13:32:42"
+        }
+    ],
     "packages-dev": [],
     "aliases": [],
     "minimum-stability": "stable",
-    "stability-flags": [],
+    "stability-flags": {
+        "google/auth": 20
+    },
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": {
diff --git a/src/php/tests/interop/interop_client.php b/src/php/tests/interop/interop_client.php
index 6f81bfa..2c1c13c 100755
--- a/src/php/tests/interop/interop_client.php
+++ b/src/php/tests/interop/interop_client.php
@@ -45,7 +45,7 @@
  * @param $error_message Message to display if the assertion is false
  */
 function hardAssert($value, $error_message) {
-  if(!$value) {
+  if (!$value) {
     echo $error_message . "\n";
     exit(1);
   }
@@ -53,7 +53,7 @@
 
 /**
  * Run the empty_unary test.
- * Currently not tested against any server as of 2014-12-04
+ * Passes when run against the Node server as of 2015-04-30
  * @param $stub Stub object that has service methods
  */
 function emptyUnary($stub) {
@@ -64,11 +64,20 @@
 
 /**
  * Run the large_unary test.
- * Passes when run against the C++ server as of 2014-12-04
- * Not tested against any other server as of 2014-12-04
+ * Passes when run against the C++/Node server as of 2015-04-30
  * @param $stub Stub object that has service methods
  */
 function largeUnary($stub) {
+  performLargeUnary($stub);
+}
+
+/**
+ * Shared code between large unary test and auth test
+ * @param $stub Stub object that has service methods
+ * @param $fillUsername boolean whether to fill result with username
+ * @param $fillOauthScope boolean whether to fill result with oauth scope
+ */
+function performLargeUnary($stub, $fillUsername = false, $fillOauthScope = false) {
   $request_len = 271828;
   $response_len = 314159;
 
@@ -79,6 +88,8 @@
   $payload->setType(grpc\testing\PayloadType::COMPRESSABLE);
   $payload->setBody(str_repeat("\0", $request_len));
   $request->setPayload($payload);
+  $request->setFillUsername($fillUsername);
+  $request->setFillOauthScope($fillOauthScope);
 
   list($result, $status) = $stub->UnaryCall($request)->wait();
   hardAssert($status->code === Grpc\STATUS_OK, 'Call did not complete successfully');
@@ -90,6 +101,27 @@
          'Payload had the wrong length');
   hardAssert($payload->getBody() === str_repeat("\0", $response_len),
          'Payload had the wrong content');
+  return $result;
+}
+
+/**
+ * Run the service account credentials auth test.
+ * Passes when run against the cloud server as of 2015-04-30
+ * @param $stub Stub object that has service methods
+ * @param $args array command line args
+ */
+function serviceAccountCreds($stub, $args) {
+  if (!array_key_exists('oauth_scope', $args)) {
+    throw new Exception('Missing oauth scope');
+  }
+  $jsonKey = json_decode(
+      file_get_contents(getenv(Google\Auth\CredentialsLoader::ENV_VAR)),
+      true);
+  $result = performLargeUnary($stub, $fillUsername=true, $fillOauthScope=true);
+  hardAssert($result->getUsername() == $jsonKey['client_email'],
+             'invalid email returned');
+  hardAssert(strpos($args['oauth_scope'], $result->getOauthScope()) !== false,
+             'invalid oauth scope returned');
 }
 
 /**
@@ -201,7 +233,8 @@
              'Call status was not CANCELLED');
 }
 
-$args = getopt('', array('server_host:', 'server_port:', 'test_case:'));
+$args = getopt('', array('server_host:', 'server_port:', 'test_case:',
+                         'server_host_override:', 'oauth_scope:'));
 if (!array_key_exists('server_host', $args) ||
     !array_key_exists('server_port', $args) ||
     !array_key_exists('test_case', $args)) {
@@ -210,20 +243,37 @@
 
 $server_address = $args['server_host'] . ':' . $args['server_port'];
 
-$credentials = Grpc\Credentials::createSsl(
-    file_get_contents(dirname(__FILE__) . '/../data/ca.pem'));
+if (!array_key_exists('server_host_override', $args)) {
+  $args['server_host_override'] = 'foo.test.google.fr';
+}
+
+$ssl_cert_file = getenv('SSL_CERT_FILE');
+if (!$ssl_cert_file) {
+  $ssl_cert_file = dirname(__FILE__) . '/../data/ca.pem';
+}
+
+$credentials = Grpc\Credentials::createSsl(file_get_contents($ssl_cert_file));
+
+$opts = [
+    'grpc.ssl_target_name_override' => $args['server_host_override'],
+    'credentials' => $credentials,
+         ];
+
+if (array_key_exists('oauth_scope', $args)) {
+  $auth = Google\Auth\ApplicationDefaultCredentials::getCredentials(
+      $args['oauth_scope']);
+  $opts['update_metadata'] = $auth->getUpdateMetadataFunc();
+}
+
 $stub = new grpc\testing\TestServiceClient(
     new Grpc\BaseStub(
         $server_address,
-        [
-            'grpc.ssl_target_name_override' => 'foo.test.google.fr',
-            'credentials' => $credentials
-         ]));
+        $opts));
 
 echo "Connecting to $server_address\n";
 echo "Running test case $args[test_case]\n";
 
-switch($args['test_case']) {
+switch ($args['test_case']) {
   case 'empty_unary':
     emptyUnary($stub);
     break;
@@ -242,6 +292,9 @@
   case 'cancel_after_first_response':
     cancelAfterFirstResponse($stub);
     break;
+  case 'service_account_creds':
+    serviceAccountCreds($stub, $args);
+    break;
   default:
     exit(1);
 }