def filter(self, environ, params, unused):
pass<EOL>
Performs final route filtering.  Should add additional
parameters to the `params` dict that should be used when
looking up the bucket.  Parameters that should be added to
params, but which should not be used to look up the bucket,
may be returned as a dictionary.  If this limit should not be
applied to this request, raise DeferLimit.  Note that
parameters that have already been filtered out of `params`
will be present in the `unused` dictionary, and will be
automatically added back to `params` after generation of the
key.

Note that the Turnstile configuration is available in the
environment under the "turnstile.conf" key.