chore: blacken (#375)

diff --git a/google/auth/crypt/__init__.py b/google/auth/crypt/__init__.py
index 7baa206..bf66e71 100644
--- a/google/auth/crypt/__init__.py
+++ b/google/auth/crypt/__init__.py
@@ -39,12 +39,7 @@
 from google.auth.crypt import rsa
 
 
-__all__ = [
-    'RSASigner',
-    'RSAVerifier',
-    'Signer',
-    'Verifier',
-]
+__all__ = ["RSASigner", "RSAVerifier", "Signer", "Verifier"]
 
 # Aliases to maintain the v1.0.0 interface, as the crypt module was split
 # into submodules.
diff --git a/google/auth/crypt/_cryptography_rsa.py b/google/auth/crypt/_cryptography_rsa.py
index 87076b0..285cf5c 100644
--- a/google/auth/crypt/_cryptography_rsa.py
+++ b/google/auth/crypt/_cryptography_rsa.py
@@ -31,18 +31,18 @@
 from google.auth.crypt import base
 
 _IMPORT_ERROR_MSG = (
-    'cryptography>=1.4.0 is required to use cryptography-based RSA '
-    'implementation.')
+    "cryptography>=1.4.0 is required to use cryptography-based RSA " "implementation."
+)
 
 try:  # pragma: NO COVER
-    release = pkg_resources.get_distribution('cryptography').parsed_version
-    if release < pkg_resources.parse_version('1.4.0'):
+    release = pkg_resources.get_distribution("cryptography").parsed_version
+    if release < pkg_resources.parse_version("1.4.0"):
         raise ImportError(_IMPORT_ERROR_MSG)
 except pkg_resources.DistributionNotFound:  # pragma: NO COVER
     raise ImportError(_IMPORT_ERROR_MSG)
 
 
-_CERTIFICATE_MARKER = b'-----BEGIN CERTIFICATE-----'
+_CERTIFICATE_MARKER = b"-----BEGIN CERTIFICATE-----"
 _BACKEND = backends.default_backend()
 _PADDING = padding.PKCS1v15()
 _SHA256 = hashes.SHA256()
@@ -88,12 +88,12 @@
 
         if _CERTIFICATE_MARKER in public_key_data:
             cert = cryptography.x509.load_pem_x509_certificate(
-                public_key_data, _BACKEND)
+                public_key_data, _BACKEND
+            )
             pubkey = cert.public_key()
 
         else:
-            pubkey = serialization.load_pem_public_key(
-                public_key_data, _BACKEND)
+            pubkey = serialization.load_pem_public_key(public_key_data, _BACKEND)
 
         return cls(pubkey)
 
@@ -122,8 +122,7 @@
     @_helpers.copy_docstring(base.Signer)
     def sign(self, message):
         message = _helpers.to_bytes(message)
-        return self._key.sign(
-            message, _PADDING, _SHA256)
+        return self._key.sign(message, _PADDING, _SHA256)
 
     @classmethod
     def from_string(cls, key, key_id=None):
@@ -145,5 +144,6 @@
         """
         key = _helpers.to_bytes(key)
         private_key = serialization.load_pem_private_key(
-            key, password=None, backend=_BACKEND)
+            key, password=None, backend=_BACKEND
+        )
         return cls(private_key, key_id=key_id)
diff --git a/google/auth/crypt/_python_rsa.py b/google/auth/crypt/_python_rsa.py
index 44aa791..d53991c 100644
--- a/google/auth/crypt/_python_rsa.py
+++ b/google/auth/crypt/_python_rsa.py
@@ -32,11 +32,9 @@
 from google.auth.crypt import base
 
 _POW2 = (128, 64, 32, 16, 8, 4, 2, 1)
-_CERTIFICATE_MARKER = b'-----BEGIN CERTIFICATE-----'
-_PKCS1_MARKER = ('-----BEGIN RSA PRIVATE KEY-----',
-                 '-----END RSA PRIVATE KEY-----')
-_PKCS8_MARKER = ('-----BEGIN PRIVATE KEY-----',
-                 '-----END PRIVATE KEY-----')
+_CERTIFICATE_MARKER = b"-----BEGIN CERTIFICATE-----"
+_PKCS1_MARKER = ("-----BEGIN RSA PRIVATE KEY-----", "-----END RSA PRIVATE KEY-----")
+_PKCS8_MARKER = ("-----BEGIN PRIVATE KEY-----", "-----END PRIVATE KEY-----")
 _PKCS8_SPEC = PrivateKeyInfo()
 
 
@@ -55,9 +53,8 @@
     num_bits = len(bit_list)
     byte_vals = bytearray()
     for start in six.moves.xrange(0, num_bits, 8):
-        curr_bits = bit_list[start:start + 8]
-        char_val = sum(
-            val * digit for val, digit in six.moves.zip(_POW2, curr_bits))
+        curr_bits = bit_list[start : start + 8]
+        char_val = sum(val * digit for val, digit in six.moves.zip(_POW2, curr_bits))
         byte_vals.append(char_val)
     return bytes(byte_vals)
 
@@ -101,16 +98,16 @@
 
         # If this is a certificate, extract the public key info.
         if is_x509_cert:
-            der = rsa.pem.load_pem(public_key, 'CERTIFICATE')
+            der = rsa.pem.load_pem(public_key, "CERTIFICATE")
             asn1_cert, remaining = decoder.decode(der, asn1Spec=Certificate())
-            if remaining != b'':
-                raise ValueError('Unused bytes', remaining)
+            if remaining != b"":
+                raise ValueError("Unused bytes", remaining)
 
-            cert_info = asn1_cert['tbsCertificate']['subjectPublicKeyInfo']
-            key_bytes = _bit_list_to_bytes(cert_info['subjectPublicKey'])
-            pubkey = rsa.PublicKey.load_pkcs1(key_bytes, 'DER')
+            cert_info = asn1_cert["tbsCertificate"]["subjectPublicKeyInfo"]
+            key_bytes = _bit_list_to_bytes(cert_info["subjectPublicKey"])
+            pubkey = rsa.PublicKey.load_pkcs1(key_bytes, "DER")
         else:
-            pubkey = rsa.PublicKey.load_pkcs1(public_key, 'PEM')
+            pubkey = rsa.PublicKey.load_pkcs1(public_key, "PEM")
         return cls(pubkey)
 
 
@@ -136,7 +133,7 @@
     @_helpers.copy_docstring(base.Signer)
     def sign(self, message):
         message = _helpers.to_bytes(message)
-        return rsa.pkcs1.sign(message, self._key, 'SHA-256')
+        return rsa.pkcs1.sign(message, self._key, "SHA-256")
 
     @classmethod
     def from_string(cls, key, key_id=None):
@@ -155,22 +152,22 @@
         """
         key = _helpers.from_bytes(key)  # PEM expects str in Python 3
         marker_id, key_bytes = pem.readPemBlocksFromFile(
-            six.StringIO(key), _PKCS1_MARKER, _PKCS8_MARKER)
+            six.StringIO(key), _PKCS1_MARKER, _PKCS8_MARKER
+        )
 
         # Key is in pkcs1 format.
         if marker_id == 0:
-            private_key = rsa.key.PrivateKey.load_pkcs1(
-                key_bytes, format='DER')
+            private_key = rsa.key.PrivateKey.load_pkcs1(key_bytes, format="DER")
         # Key is in pkcs8.
         elif marker_id == 1:
-            key_info, remaining = decoder.decode(
-                key_bytes, asn1Spec=_PKCS8_SPEC)
-            if remaining != b'':
-                raise ValueError('Unused bytes', remaining)
-            private_key_info = key_info.getComponentByName('privateKey')
+            key_info, remaining = decoder.decode(key_bytes, asn1Spec=_PKCS8_SPEC)
+            if remaining != b"":
+                raise ValueError("Unused bytes", remaining)
+            private_key_info = key_info.getComponentByName("privateKey")
             private_key = rsa.key.PrivateKey.load_pkcs1(
-                private_key_info.asOctets(), format='DER')
+                private_key_info.asOctets(), format="DER"
+            )
         else:
-            raise ValueError('No key could be detected.')
+            raise ValueError("No key could be detected.")
 
         return cls(private_key, key_id=key_id)
diff --git a/google/auth/crypt/base.py b/google/auth/crypt/base.py
index c6c0427..ceb6e9c 100644
--- a/google/auth/crypt/base.py
+++ b/google/auth/crypt/base.py
@@ -21,8 +21,8 @@
 import six
 
 
-_JSON_FILE_PRIVATE_KEY = 'private_key'
-_JSON_FILE_PRIVATE_KEY_ID = 'private_key_id'
+_JSON_FILE_PRIVATE_KEY = "private_key"
+_JSON_FILE_PRIVATE_KEY_ID = "private_key_id"
 
 
 @six.add_metaclass(abc.ABCMeta)
@@ -43,7 +43,7 @@
         """
         # pylint: disable=missing-raises-doc,redundant-returns-doc
         # (pylint doesn't recognize that this is abstract)
-        raise NotImplementedError('Verify must be implemented')
+        raise NotImplementedError("Verify must be implemented")
 
 
 @six.add_metaclass(abc.ABCMeta)
@@ -53,7 +53,7 @@
     @abc.abstractproperty
     def key_id(self):
         """Optional[str]: The key ID used to identify this private key."""
-        raise NotImplementedError('Key id must be implemented')
+        raise NotImplementedError("Key id must be implemented")
 
     @abc.abstractmethod
     def sign(self, message):
@@ -67,7 +67,7 @@
         """
         # pylint: disable=missing-raises-doc,redundant-returns-doc
         # (pylint doesn't recognize that this is abstract)
-        raise NotImplementedError('Sign must be implemented')
+        raise NotImplementedError("Sign must be implemented")
 
 
 @six.add_metaclass(abc.ABCMeta)
@@ -88,7 +88,7 @@
         Raises:
             ValueError: If the key cannot be parsed.
         """
-        raise NotImplementedError('from_string must be implemented')
+        raise NotImplementedError("from_string must be implemented")
 
     @classmethod
     def from_service_account_info(cls, info):
@@ -107,12 +107,12 @@
         """
         if _JSON_FILE_PRIVATE_KEY not in info:
             raise ValueError(
-                'The private_key field was not found in the service account '
-                'info.')
+                "The private_key field was not found in the service account " "info."
+            )
 
         return cls.from_string(
-            info[_JSON_FILE_PRIVATE_KEY],
-            info.get(_JSON_FILE_PRIVATE_KEY_ID))
+            info[_JSON_FILE_PRIVATE_KEY], info.get(_JSON_FILE_PRIVATE_KEY_ID)
+        )
 
     @classmethod
     def from_service_account_file(cls, filename):
@@ -125,7 +125,7 @@
         Returns:
             google.auth.crypt.Signer: The constructed signer.
         """
-        with io.open(filename, 'r', encoding='utf-8') as json_file:
+        with io.open(filename, "r", encoding="utf-8") as json_file:
             data = json.load(json_file)
 
         return cls.from_service_account_info(data)