diff --git a/google/auth/_helpers.py b/google/auth/_helpers.py
index 5a6c3a8..de86bee 100644
--- a/google/auth/_helpers.py
+++ b/google/auth/_helpers.py
@@ -14,6 +14,7 @@
 
 """Helper functions for commonly used utilities."""
 
+import base64
 import calendar
 import datetime
 
@@ -194,3 +195,19 @@
         return []
 
     return scopes.split(' ')
+
+
+def padded_urlsafe_b64decode(value):
+    """Decodes base64 strings lacking padding characters.
+
+    Google infrastructure tends to omit the base64 padding characters.
+
+    Args:
+        value (Union[str, bytes]): The encoded value.
+
+    Returns:
+        bytes: The decoded value
+    """
+    b64string = to_bytes(value)
+    padded = b64string + b'=' * (-len(b64string) % 4)
+    return base64.urlsafe_b64decode(padded)
diff --git a/google/auth/jwt.py b/google/auth/jwt.py
index 7abe4c2..0884b3d 100644
--- a/google/auth/jwt.py
+++ b/google/auth/jwt.py
@@ -96,7 +96,7 @@
 
 def _decode_jwt_segment(encoded_section):
     """Decodes a single JWT segment."""
-    section_bytes = base64.urlsafe_b64decode(encoded_section)
+    section_bytes = _helpers.padded_urlsafe_b64decode(encoded_section)
     try:
         return json.loads(section_bytes.decode('utf-8'))
     except ValueError:
@@ -124,7 +124,7 @@
 
     encoded_header, encoded_payload, signature = token.split(b'.')
     signed_section = encoded_header + b'.' + encoded_payload
-    signature = base64.urlsafe_b64decode(signature)
+    signature = _helpers.padded_urlsafe_b64decode(signature)
 
     # Parse segments
     header = _decode_jwt_segment(encoded_header)
diff --git a/google/oauth2/id_token.py b/google/oauth2/id_token.py
index 968f271..fa96fc0 100644
--- a/google/oauth2/id_token.py
+++ b/google/oauth2/id_token.py
@@ -47,7 +47,7 @@
         Mapping[str, str]: A mapping of public key ID to x.509 certificate
             data.
     """
-    response = request('GET', certs_url)
+    response = request(certs_url, method='GET')
 
     if response.status != http_client.OK:
         raise exceptions.TransportError(