[Ace] draft-ietf-ace-mqtt-tls-profile - Validating a subscription is in scope

[Jim Schaad <[e-mail]>]

I have run across an interesting question for doing validation of
subscriptions that I would like to get an opinion on.

When doing a publish, there is not an issue.  One simply takes the set of
values in the scope field as topic filters and checks the publication topic
against the set of permissible publication topic filters in the scope.

When doing a subscribe, there are four distinct cases that can arise:
1.  The subscription is for a single topic and either is or is not
successfully matched against the scope topic filter.
2.  The subscription is for a topic filter and it is identical to the scope
topic filter.
3.  Both are topic filters and are not the same.  Is one supposed to do some
type of subset matching on the two filters or does one always say that this
is not a match.  This is not addressed in the MQTT document and I am not
sure where it would be addressed.   As an example:

Scope value is subscribe_sport/#
Subscription topic is sport/tennis/#

The second is clearly a subset of the first and thus it would seem logical
to include it, but it gets more complicated if one instead asks for

Subscription topic is sport/+

In this case the two wild cards are not the same value.

Jim