This plugin allows you to create template tags containing the connecting
IPs AS number and route info for that AS number.
The default config will add a header field that looks like this:
X-Spam-ASN: AS24940 184.108.40.206/18
where 24940 is the ASN and 220.127.116.11/18 is the route
announced by that ASN where the connecting IP address came from.
If the AS announces multiple networks (more/less specific), they will
all be added to the _ASNCIDR_ tag, separated by spaces, eg:
X-Spam-ASN: AS1680 18.104.22.168/15 22.214.171.124/16
Note that the literal AS before the ASN in the _ASN_ tag is configurable
through the asn_prefix directive and may be set to an empty string.