'Add the resource owner password and username 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 in the HTTP request entity-body:
grant_type
REQUIRED.  Value MUST be set to "password".
username
REQUIRED.  The resource owner username.
password
REQUIRED.  The resource owner password.
scope
OPTIONAL.  The scope of the access request as described by
`Section 3.3`_.
.. _`Section 3.3`: http://tools.ietf.org/html/draft-ietf-oauth-v2-28#section-3.3'

def prepare_request_body(self, username, password, body=u'', scope=None, **kwargs):

    return prepare_token_request(u'password', body=body, username=username, password=password, scope=scope, **kwargs)
