From d9d548a9ccfd857362566ffb6c5b46721205b438 Mon Sep 17 00:00:00 2001
From: Mark Pellegrini <markpell@google.com>
Date: Fri, 20 Jun 2014 10:58:19 -0400
Subject: [PATCH] Clone headers before setting user-agent to preserve the
 semantics of httplib2 request method

---
 oauth2client/client.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/oauth2client/client.py b/oauth2client/client.py
index a3af4f8..7301dd9 100644
--- a/oauth2client/client.py
+++ b/oauth2client/client.py
@@ -490,10 +490,12 @@ class OAuth2Credentials(Credentials):
         logger.info('Attempting refresh to obtain initial access_token')
         self._refresh(request_orig)
 
-      # Modify the request headers to add the appropriate
+      # Clone and modify the request headers to add the appropriate
       # Authorization header.
       if headers is None:
         headers = {}
+      else:
+        headers = dict(headers)
       self.apply(headers)
 
       if self.user_agent is not None: