Initial python3 changes

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

lib/oauthlib/oauth2/rfc6749/clients/backend_application.py

@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+"""
+oauthlib.oauth2.rfc6749
+~~~~~~~~~~~~~~~~~~~~~~~
+
+This module is an implementation of various logic needed
+for consuming and providing OAuth 2.0 RFC6749.
+"""
+from ..parameters import prepare_token_request
+from .base import Client
+
+
+class BackendApplicationClient(Client):
+
+    """A public client utilizing the client credentials grant workflow.
+
+    The client can request an access token using only its client
+    credentials (or other supported means of authentication) when the
+    client is requesting access to the protected resources under its
+    control, or those of another resource owner which has been previously
+    arranged with the authorization server (the method of which is beyond
+    the scope of this specification).
+
+    The client credentials grant type MUST only be used by confidential
+    clients.
+
+    Since the client authentication is used as the authorization grant,
+    no additional authorization request is needed.
+    """
+
+    grant_type = 'client_credentials'
+
+    def prepare_request_body(self, body='', scope=None,
+                             include_client_id=False, **kwargs):
+        """Add the client credentials to the request body.
+
+        The client makes a request to the token endpoint by adding the
+        following parameters using the "application/x-www-form-urlencoded"
+        format per `Appendix B`_ in the HTTP request entity-body:
+
+        :param body: Existing request body (URL encoded string) to embed parameters
+                     into. This may contain extra paramters. Default ''.
+        :param scope:   The scope of the access request as described by
+                        `Section 3.3`_.
+
+        :param include_client_id: `True` to send the `client_id` in the
+                                  body of the upstream request. This is required
+                                  if the client is not authenticating with the
+                                  authorization server as described in
+                                  `Section 3.2.1`_. False otherwise (default).
+        :type include_client_id: Boolean
+
+        :param kwargs:  Extra credentials to include in the token request.
+
+        The client MUST authenticate with the authorization server as
+        described in `Section 3.2.1`_.
+
+        The prepared body will include all provided credentials as well as
+        the ``grant_type`` parameter set to ``client_credentials``::
+
+            >>> from oauthlib.oauth2 import BackendApplicationClient
+            >>> client = BackendApplicationClient('your_id')
+            >>> client.prepare_request_body(scope=['hello', 'world'])
+            'grant_type=client_credentials&scope=hello+world'
+
+        .. _`Appendix B`: https://tools.ietf.org/html/rfc6749#appendix-B
+        .. _`Section 3.3`: https://tools.ietf.org/html/rfc6749#section-3.3
+        .. _`Section 3.2.1`: https://tools.ietf.org/html/rfc6749#section-3.2.1
+        """
+        kwargs['client_id'] = self.client_id
+        kwargs['include_client_id'] = include_client_id
+        scope = self.scope if scope is None else scope
+        return prepare_token_request(self.grant_type, body=body,
+                                     scope=scope, **kwargs)