From bd0ccc5fe77d55f7a19f5278d6b60587c393ee3c Mon Sep 17 00:00:00 2001
From: arithmetic1728 <58957152+arithmetic1728@users.noreply.github.com>
Date: Mon, 1 Nov 2021 10:22:26 -0700
Subject: fix: use 'int.to_bytes' and 'int.from_bytes' for py3 (#904)

---
 google/auth/_helpers.py    | 10 ++++++++++
 google/auth/crypt/es256.py | 18 +++++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/google/auth/_helpers.py b/google/auth/_helpers.py
index b239fcd..1b08ab8 100644
--- a/google/auth/_helpers.py
+++ b/google/auth/_helpers.py
@@ -17,6 +17,7 @@
 import base64
 import calendar
 import datetime
+import sys
 
 import six
 from six.moves import urllib
@@ -233,3 +234,12 @@ def unpadded_urlsafe_b64encode(value):
         Union[str|bytes]: The encoded value
     """
     return base64.urlsafe_b64encode(value).rstrip(b"=")
+
+
+def is_python_3():
+    """Check if the Python interpreter is Python 2 or 3.
+
+    Returns:
+        bool: True if the Python interpreter is Python 3 and False otherwise.
+    """
+    return sys.version_info > (3, 0)
diff --git a/google/auth/crypt/es256.py b/google/auth/crypt/es256.py
index c6d6176..42823a7 100644
--- a/google/auth/crypt/es256.py
+++ b/google/auth/crypt/es256.py
@@ -53,8 +53,16 @@ class ES256Verifier(base.Verifier):
         sig_bytes = _helpers.to_bytes(signature)
         if len(sig_bytes) != 64:
             return False
-        r = utils.int_from_bytes(sig_bytes[:32], byteorder="big")
-        s = utils.int_from_bytes(sig_bytes[32:], byteorder="big")
+        r = (
+            int.from_bytes(sig_bytes[:32], byteorder="big")
+            if _helpers.is_python_3()
+            else utils.int_from_bytes(sig_bytes[:32], byteorder="big")
+        )
+        s = (
+            int.from_bytes(sig_bytes[32:], byteorder="big")
+            if _helpers.is_python_3()
+            else utils.int_from_bytes(sig_bytes[32:], byteorder="big")
+        )
         asn1_sig = encode_dss_signature(r, s)
 
         message = _helpers.to_bytes(message)
@@ -121,7 +129,11 @@ class ES256Signer(base.Signer, base.FromServiceAccountMixin):
 
         # Convert ASN1 encoded signature to (r||s) raw signature.
         (r, s) = decode_dss_signature(asn1_signature)
-        return utils.int_to_bytes(r, 32) + utils.int_to_bytes(s, 32)
+        return (
+            (r.to_bytes(32, byteorder="big") + s.to_bytes(32, byteorder="big"))
+            if _helpers.is_python_3()
+            else (utils.int_to_bytes(r, 32) + utils.int_to_bytes(s, 32))
+        )
 
     @classmethod
     def from_string(cls, key, key_id=None):
-- 
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