Add google.auth.jwt (#7)

diff --git a/google/auth/_helpers.py b/google/auth/_helpers.py
index 2d3b653..0a62209 100644
--- a/google/auth/_helpers.py
+++ b/google/auth/_helpers.py
@@ -14,9 +14,34 @@
 
 """Helper functions for commonly used utilities."""
 
+
+import calendar
+import datetime
+
 import six
 
 
+def utcnow():
+    """Returns the current UTC datetime.
+
+    Returns:
+        datetime: The current time in UTC.
+    """
+    return datetime.datetime.utcnow()
+
+
+def datetime_to_secs(value):
+    """Convert a datetime object to the number of seconds since the UNIX epoch.
+
+    Args:
+        value (datetime): The datetime to convert.
+
+    Returns:
+        int: The number of seconds since the UNIX epoch.
+    """
+    return calendar.timegm(value.utctimetuple())
+
+
 def to_bytes(value, encoding='utf-8'):
     """Converts a string value to bytes, if necessary.