chore: blacken (#375)

diff --git a/system_tests/noxfile.py b/system_tests/noxfile.py
index fa0422a..5f9291a 100644
--- a/system_tests/noxfile.py
+++ b/system_tests/noxfile.py
@@ -30,31 +30,31 @@
 
 
 HERE = os.path.abspath(os.path.dirname(__file__))
-DATA_DIR = os.path.join(HERE, 'data')
-SERVICE_ACCOUNT_FILE = os.path.join(DATA_DIR, 'service_account.json')
-AUTHORIZED_USER_FILE = os.path.join(DATA_DIR, 'authorized_user.json')
-EXPLICIT_CREDENTIALS_ENV = 'GOOGLE_APPLICATION_CREDENTIALS'
-EXPLICIT_PROJECT_ENV = 'GOOGLE_CLOUD_PROJECT'
-EXPECT_PROJECT_ENV = 'EXPECT_PROJECT_ID'
+DATA_DIR = os.path.join(HERE, "data")
+SERVICE_ACCOUNT_FILE = os.path.join(DATA_DIR, "service_account.json")
+AUTHORIZED_USER_FILE = os.path.join(DATA_DIR, "authorized_user.json")
+EXPLICIT_CREDENTIALS_ENV = "GOOGLE_APPLICATION_CREDENTIALS"
+EXPLICIT_PROJECT_ENV = "GOOGLE_CLOUD_PROJECT"
+EXPECT_PROJECT_ENV = "EXPECT_PROJECT_ID"
 
-SKIP_GAE_TEST_ENV = 'SKIP_APP_ENGINE_SYSTEM_TEST'
-GAE_APP_URL_TMPL = 'https://{}-dot-{}.appspot.com'
-GAE_TEST_APP_SERVICE = 'google-auth-system-tests'
+SKIP_GAE_TEST_ENV = "SKIP_APP_ENGINE_SYSTEM_TEST"
+GAE_APP_URL_TMPL = "https://{}-dot-{}.appspot.com"
+GAE_TEST_APP_SERVICE = "google-auth-system-tests"
 
 # The download location for the Cloud SDK
-CLOUD_SDK_DIST_FILENAME = 'google-cloud-sdk.tar.gz'
-CLOUD_SDK_DOWNLOAD_URL = (
-    'https://dl.google.com/dl/cloudsdk/release/{}'.format(
-        CLOUD_SDK_DIST_FILENAME))
+CLOUD_SDK_DIST_FILENAME = "google-cloud-sdk.tar.gz"
+CLOUD_SDK_DOWNLOAD_URL = "https://dl.google.com/dl/cloudsdk/release/{}".format(
+    CLOUD_SDK_DIST_FILENAME
+)
 
 # This environment variable is recognized by the Cloud SDK and overrides
 # the location of the SDK's configuration files (which is usually at
 # ${HOME}/.config).
-CLOUD_SDK_CONFIG_ENV = 'CLOUDSDK_CONFIG'
+CLOUD_SDK_CONFIG_ENV = "CLOUDSDK_CONFIG"
 
 # If set, this is where the environment setup will install the Cloud SDK.
 # If unset, it will download the SDK to a temporary directory.
-CLOUD_SDK_ROOT = os.environ.get('CLOUD_SDK_ROOT')
+CLOUD_SDK_ROOT = os.environ.get("CLOUD_SDK_ROOT")
 
 if CLOUD_SDK_ROOT is not None:
     CLOUD_SDK_ROOT = py.path.local(CLOUD_SDK_ROOT)
@@ -63,15 +63,15 @@
     CLOUD_SDK_ROOT = py.path.local.mkdtemp()
 
 # The full path the cloud sdk install directory
-CLOUD_SDK_INSTALL_DIR = CLOUD_SDK_ROOT.join('google-cloud-sdk')
+CLOUD_SDK_INSTALL_DIR = CLOUD_SDK_ROOT.join("google-cloud-sdk")
 
 # The full path to the gcloud cli executable.
-GCLOUD = str(CLOUD_SDK_INSTALL_DIR.join('bin', 'gcloud'))
+GCLOUD = str(CLOUD_SDK_INSTALL_DIR.join("bin", "gcloud"))
 
 # gcloud requires Python 2 and doesn't work on 3, so we need to tell it
 # where to find 2 when we're running in a 3 environment.
-CLOUD_SDK_PYTHON_ENV = 'CLOUDSDK_PYTHON'
-CLOUD_SDK_PYTHON = which('python2', None)
+CLOUD_SDK_PYTHON_ENV = "CLOUDSDK_PYTHON"
+CLOUD_SDK_PYTHON = which("python2", None)
 
 # Cloud SDK helpers
 
@@ -87,46 +87,47 @@
     session.env[CLOUD_SDK_PYTHON_ENV] = CLOUD_SDK_PYTHON
     # This set the $PATH for the subprocesses so they can find the gcloud
     # executable.
-    session.env['PATH'] = (
-        str(CLOUD_SDK_INSTALL_DIR.join('bin')) + os.pathsep +
-        os.environ['PATH'])
+    session.env["PATH"] = (
+        str(CLOUD_SDK_INSTALL_DIR.join("bin")) + os.pathsep + os.environ["PATH"]
+    )
 
     # If gcloud cli executable already exists, just update it.
     if py.path.local(GCLOUD).exists():
-        session.run(GCLOUD, 'components', 'update', '-q')
+        session.run(GCLOUD, "components", "update", "-q")
         return
 
     tar_path = CLOUD_SDK_ROOT.join(CLOUD_SDK_DIST_FILENAME)
 
     # Download the release.
-    session.run(
-        'wget', CLOUD_SDK_DOWNLOAD_URL, '-O', str(tar_path), silent=True)
+    session.run("wget", CLOUD_SDK_DOWNLOAD_URL, "-O", str(tar_path), silent=True)
 
     # Extract the release.
-    session.run(
-        'tar', 'xzf', str(tar_path), '-C', str(CLOUD_SDK_ROOT))
+    session.run("tar", "xzf", str(tar_path), "-C", str(CLOUD_SDK_ROOT))
     session.run(tar_path.remove)
 
     # Run the install script.
     session.run(
-        str(CLOUD_SDK_INSTALL_DIR.join('install.sh')),
-        '--usage-reporting', 'false',
-        '--path-update', 'false',
-        '--command-completion', 'false',
-        silent=True)
+        str(CLOUD_SDK_INSTALL_DIR.join("install.sh")),
+        "--usage-reporting",
+        "false",
+        "--path-update",
+        "false",
+        "--command-completion",
+        "false",
+        silent=True,
+    )
 
 
 def copy_credentials(credentials_path):
     """Copies credentials into the SDK root as the application default
     credentials."""
-    dest = CLOUD_SDK_ROOT.join('application_default_credentials.json')
+    dest = CLOUD_SDK_ROOT.join("application_default_credentials.json")
     if dest.exists():
         dest.remove()
     py.path.local(credentials_path).copy(dest)
 
 
-def configure_cloud_sdk(
-        session, application_default_credentials, project=False):
+def configure_cloud_sdk(session, application_default_credentials, project=False):
     """Installs and configures the Cloud SDK with the given application default
     credentials.
 
@@ -140,13 +141,13 @@
     # change the application default credentials file, which is user
     # credentials instead of service account credentials sometimes.
     session.run(
-        GCLOUD, 'auth', 'activate-service-account', '--key-file',
-        SERVICE_ACCOUNT_FILE)
+        GCLOUD, "auth", "activate-service-account", "--key-file", SERVICE_ACCOUNT_FILE
+    )
 
     if project:
-        session.run(GCLOUD, 'config', 'set', 'project', 'example-project')
+        session.run(GCLOUD, "config", "set", "project", "example-project")
     else:
-        session.run(GCLOUD, 'config', 'unset', 'project')
+        session.run(GCLOUD, "config", "unset", "project")
 
     # Copy the credentials file to the config root. This is needed because
     # unfortunately gcloud doesn't provide a clean way to tell it to use
@@ -160,8 +161,8 @@
     # that our credentials matches the format expected by gcloud.
     # Silent is set to True to prevent leaking secrets in test logs.
     session.run(
-        GCLOUD, 'auth', 'application-default', 'print-access-token',
-        silent=True)
+        GCLOUD, "auth", "application-default", "print-access-token", silent=True
+    )
 
 
 # Test sesssions
@@ -169,99 +170,102 @@
 
 def session_service_account(session):
     session.virtualenv = False
-    session.run('pytest', 'test_service_account.py')
+    session.run("pytest", "test_service_account.py")
 
 
 def session_oauth2_credentials(session):
     session.virtualenv = False
-    session.run('pytest', 'test_oauth2_credentials.py')
+    session.run("pytest", "test_oauth2_credentials.py")
 
 
 def session_default_explicit_service_account(session):
     session.virtualenv = False
     session.env[EXPLICIT_CREDENTIALS_ENV] = SERVICE_ACCOUNT_FILE
-    session.env[EXPECT_PROJECT_ENV] = '1'
-    session.run('pytest', 'test_default.py')
+    session.env[EXPECT_PROJECT_ENV] = "1"
+    session.run("pytest", "test_default.py")
 
 
 def session_default_explicit_authorized_user(session):
     session.virtualenv = False
     session.env[EXPLICIT_CREDENTIALS_ENV] = AUTHORIZED_USER_FILE
-    session.run('pytest', 'test_default.py')
+    session.run("pytest", "test_default.py")
 
 
 def session_default_explicit_authorized_user_explicit_project(session):
     session.virtualenv = False
     session.env[EXPLICIT_CREDENTIALS_ENV] = AUTHORIZED_USER_FILE
-    session.env[EXPLICIT_PROJECT_ENV] = 'example-project'
-    session.env[EXPECT_PROJECT_ENV] = '1'
-    session.run('pytest', 'test_default.py')
+    session.env[EXPLICIT_PROJECT_ENV] = "example-project"
+    session.env[EXPECT_PROJECT_ENV] = "1"
+    session.run("pytest", "test_default.py")
 
 
 def session_default_cloud_sdk_service_account(session):
     session.virtualenv = False
     configure_cloud_sdk(session, SERVICE_ACCOUNT_FILE)
-    session.env[EXPECT_PROJECT_ENV] = '1'
-    session.run('pytest', 'test_default.py')
+    session.env[EXPECT_PROJECT_ENV] = "1"
+    session.run("pytest", "test_default.py")
 
 
 def session_default_cloud_sdk_authorized_user(session):
     session.virtualenv = False
     configure_cloud_sdk(session, AUTHORIZED_USER_FILE)
-    session.run('pytest', 'test_default.py')
+    session.run("pytest", "test_default.py")
 
 
 def session_default_cloud_sdk_authorized_user_configured_project(session):
     session.virtualenv = False
     configure_cloud_sdk(session, AUTHORIZED_USER_FILE, project=True)
-    session.env[EXPECT_PROJECT_ENV] = '1'
-    session.run('pytest', 'test_default.py')
+    session.env[EXPECT_PROJECT_ENV] = "1"
+    session.run("pytest", "test_default.py")
 
 
 def session_compute_engine(session):
     session.virtualenv = False
-    session.run('pytest', 'test_compute_engine.py')
+    session.run("pytest", "test_compute_engine.py")
 
 
 def session_app_engine(session):
     session.virtualenv = False
 
     if SKIP_GAE_TEST_ENV in os.environ:
-        session.log('Skipping App Engine tests.')
+        session.log("Skipping App Engine tests.")
         return
 
     # Unlike the default tests above, the App Engine system test require a
     # 'real' gcloud sdk installation that is configured to deploy to an
     # app engine project.
     # Grab the project ID from the cloud sdk.
-    project_id = subprocess.check_output([
-        'gcloud', 'config', 'list', 'project', '--format',
-        'value(core.project)']).decode('utf-8').strip()
+    project_id = (
+        subprocess.check_output(
+            ["gcloud", "config", "list", "project", "--format", "value(core.project)"]
+        )
+        .decode("utf-8")
+        .strip()
+    )
 
     if not project_id:
         session.error(
-            'The Cloud SDK must be installed and configured to deploy to App '
-            'Engine.')
+            "The Cloud SDK must be installed and configured to deploy to App " "Engine."
+        )
 
-    application_url = GAE_APP_URL_TMPL.format(
-        GAE_TEST_APP_SERVICE, project_id)
+    application_url = GAE_APP_URL_TMPL.format(GAE_TEST_APP_SERVICE, project_id)
 
     # Vendor in the test application's dependencies
-    session.chdir(os.path.join(HERE, 'app_engine_test_app'))
+    session.chdir(os.path.join(HERE, "app_engine_test_app"))
     session.run(
-        'pip', 'install', '--target', 'lib', '-r', 'requirements.txt',
-        silent=True)
+        "pip", "install", "--target", "lib", "-r", "requirements.txt", silent=True
+    )
 
     # Deploy the application.
-    session.run('gcloud', 'app', 'deploy', '-q', 'app.yaml')
+    session.run("gcloud", "app", "deploy", "-q", "app.yaml")
 
     # Run the tests
-    session.env['TEST_APP_URL'] = application_url
+    session.env["TEST_APP_URL"] = application_url
     session.chdir(HERE)
-    session.run('pytest', 'test_app_engine.py')
+    session.run("pytest", "test_app_engine.py")
 
 
 def session_grpc(session):
     session.virtualenv = False
     session.env[EXPLICIT_CREDENTIALS_ENV] = SERVICE_ACCOUNT_FILE
-    session.run('pytest', 'test_grpc.py')
+    session.run("pytest", "test_grpc.py")