InCommon metadata support

[Tom Scavo <>]

On the production server md.incommon.org (which serves aggregates), we
have the following attributes on the root element:

/md:EntitiesDescriptor/@validUntil? (currently 14d)
/md:EntitiesDescriptor/@cacheDuration? (currently NONE)

I've always thought the optimal validUntil value should be around 4
days but we're a long way from achieving that goal. On the Metadata
Consumption wiki page [1], we recommend that clients attempt a refresh
every hour (which is cacheDuration, right?). Since metadata is
typically signed once a day and the server supports HTTP Conditional
GET, I'm not sure that is optimal either (but I'm not too concerned
about it).

On the beta server mdq-beta.incommon.org (which serves per-entity
metadata), we have the following attributes on the root element:

/md:EntityDescriptor/@validUntil? (currently 14d)
/md:EntityDescriptor/@cacheDuration? (currently 6h)

I doubt these values are optimal. (This is a beta server, which is why
I haven't brought this up before now.) It's a fact that per-entity
metadata doesn't change near as often as aggregate metadata. Should
this fact be factored into the parameters somehow?

My gut tells me that validUntil should be large while cacheDuration
should be small. Does this sound right?

Tom

[1] https://spaces.internet2.edu/x/JwQjAQ