Create a request token response, with a new request token if valid.

        :param uri: The full URI of the token request.
        :param http_method: A valid HTTP verb, i.e. GET, POST, PUT, HEAD, etc.
        :param body: The request body as a string.
        :param headers: The request headers as a dict.
        :param credentials: A list of extra credentials to include in the token.
        :returns: A tuple of 3 elements.
                  1. A dict of headers to set on the response.
                  2. The response body as a string.
                  3. The response status code as an integer.

        An example of a valid request::

            >>> from your_validator import your_validator
            >>> from oauthlib.oauth1 import RequestTokenEndpoint
            >>> endpoint = RequestTokenEndpoint(your_validator)
            >>> h, b, s = endpoint.create_request_token_response(
            ...     'https://your.provider/request_token?foo=bar',
            ...     headers={
            ...         'Authorization': 'OAuth realm=movies user, oauth_....'
            ...     },
            ...     credentials={
            ...         'my_specific': 'argument',
            ...     })
            >>> h
            {'Content-Type': 'application/x-www-form-urlencoded'}
            >>> b
            'oauth_token=lsdkfol23w54jlksdef&oauth_token_secret=qwe089234lkjsdf&oauth_callback_confirmed=true&my_specific=argument'
            >>> s
            200

        An response to invalid request would have a different body and status::

            >>> b
            'error=invalid_request&description=missing+callback+uri'
            >>> s
            400

        The same goes for an an unauthorized request:

            >>> b
            ''
            >>> s
            401

def create_request_token_response(self, uri, http_method='GET', body=None,
                                      headers=None, credentials=None):
        """Create a request token response, with a new request token if valid.

        :param uri: The full URI of the token request.
        :param http_method: A valid HTTP verb, i.e. GET, POST, PUT, HEAD, etc.
        :param body: The request body as a string.
        :param headers: The request headers as a dict.
        :param credentials: A list of extra credentials to include in the token.
        :returns: A tuple of 3 elements.
                  1. A dict of headers to set on the response.
                  2. The response body as a string.
                  3. The response status code as an integer.

        An example of a valid request::

            >>> from your_validator import your_validator
            >>> from oauthlib.oauth1 import RequestTokenEndpoint
            >>> endpoint = RequestTokenEndpoint(your_validator)
            >>> h, b, s = endpoint.create_request_token_response(
            ...     'https://your.provider/request_token?foo=bar',
            ...     headers={
            ...         'Authorization': 'OAuth realm=movies user, oauth_....'
            ...     },
            ...     credentials={
            ...         'my_specific': 'argument',
            ...     })
            >>> h
            {'Content-Type': 'application/x-www-form-urlencoded'}
            >>> b
            'oauth_token=lsdkfol23w54jlksdef&oauth_token_secret=qwe089234lkjsdf&oauth_callback_confirmed=true&my_specific=argument'
            >>> s
            200

        An response to invalid request would have a different body and status::

            >>> b
            'error=invalid_request&description=missing+callback+uri'
            >>> s
            400

        The same goes for an an unauthorized request:

            >>> b
            ''
            >>> s
            401
        """
        resp_headers = {'Content-Type': 'application/x-www-form-urlencoded'}
        try:
            request = self._create_request(uri, http_method, body, headers)
            valid, processed_request = self.validate_request_token_request(
                request)
            if valid:
                token = self.create_request_token(request, credentials or {})
                return resp_headers, token, 200
            else:
                return {}, None, 401
        except errors.OAuth1Error as e:
            return resp_headers, e.urlencoded, e.status_code