def METHOD_NAME(self, username, password, body='', scope=None,
                         include_client_id=False, **kwargs):
    """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 per `Appendix B`_ in the HTTP request entity-body:
    :param username:    The resource owner username.
    :param password:    The resource owner password.
    :param body: Existing request body (URL encoded string) to embed parameters
                 into. This may contain extra parameters. 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.
    If the client type is confidential or the client was issued client
    credentials (or assigned other authentication requirements), 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 ``password``::
        >>> from oauthlib.oauth2 import LegacyApplicationClient
        >>> client = LegacyApplicationClient('your_id')
        >>> client.prepare_request_body(username='foo', password='bar', scope=['hello', 'world'])
        'grant_type=password&username=foo&scope=hello+world&password=bar'
    .. _`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, username=username,
                                 password=password, scope=scope, **kwargs)