Allow caching of /.well-known/browserid

[rfk]

Because otherwise the verifier will have to fetch it for every validation; we want to add some verifier-side caching per https://bugzilla.mozilla.org/show_bug.cgi?id=977922

We currently serve it with header Cache-Control: no-cache. A good place to start might be copying persona.org, which services its support document with Cache-Control: public, max-age=10.

[gene1wood]

I've confirmed that the cache-control is being set by node, not nginx so this change will need to happen in the app

[mostlygeek]

@dannycoates is "10000" an arbitrary value or does it have some sort of significance?

[dannycoates]

max-age=10 is what persona.org uses, arbitrary but changeable.

[mostlygeek]

Oh, that's in milliseconds. OK yah even living in the cache for 10 seconds would drop our traffic usage down by a lot!