Build redirect url for a given provider.

def get_redirect_url(self, **kwargs):
        "Build redirect url for a given provider."
        name = kwargs.get('provider', '')
        try:
            provider = Provider.objects.get(name=name)
        except Provider.DoesNotExist:
            raise Http404('Unknown OAuth provider.')
        else:
            if not provider.enabled():
                raise Http404('Provider %s is not enabled.' % name)
            client = self.get_client(provider)
            callback = self.get_callback_url(provider)
            params = self.get_additional_parameters(provider)
            return client.get_redirect_url(self.request, callback=callback, parameters=params)