Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/requests_oauthlib/oauth2_auth.py

@@ -0,0 +1,37 @@
+from __future__ import unicode_literals
+from oauthlib.oauth2 import WebApplicationClient, InsecureTransportError
+from oauthlib.oauth2 import is_secure_transport
+from requests.auth import AuthBase
+
+
+class OAuth2(AuthBase):
+    """Adds proof of authorization (OAuth2 token) to the request."""
+
+    def __init__(self, client_id=None, client=None, token=None):
+        """Construct a new OAuth 2 authorization object.
+
+        :param client_id: Client id obtained during registration
+        :param client: :class:`oauthlib.oauth2.Client` to be used. Default is
+                       WebApplicationClient which is useful for any
+                       hosted application but not mobile or desktop.
+        :param token: Token dictionary, must include access_token
+                      and token_type.
+        """
+        self._client = client or WebApplicationClient(client_id, token=token)
+        if token:
+            for k, v in token.items():
+                setattr(self._client, k, v)
+
+    def __call__(self, r):
+        """Append an OAuth 2 token to the request.
+
+        Note that currently HTTPS is required for all requests. There may be
+        a token type that allows for plain HTTP in the future and then this
+        should be updated to allow plain HTTP on a white list basis.
+        """
+        if not is_secure_transport(r.url):
+            raise InsecureTransportError()
+        r.url, r.headers, r.body = self._client.add_token(
+            r.url, http_method=r.method, body=r.body, headers=r.headers
+        )
+        return r