def get_redirect_url(self, **kwargs):
        """Build redirect url for a given provider."""
        provider_id = kwargs.get('provider', '')
        provider = self.get_provider(provider_id)
        if not provider:
            raise Http404('Unknown OAuth provider.')
        callback = self.get_callback_url(provider)
        params = self.get_additional_parameters(provider)
        return provider.get_redirect_url(self.request, callback=callback, parameters=params)