current logic is not safe as it will allow an IP that isnt persisted to
the DB to be given out multiple times if machines joins in quick
succession.
This adds a lock around the "get ip" and machine registration and save
to DB so we ensure thiis isnt happning.
Currently this had to be done three places, which is silly, and outlined
in #294.
This commit converts all the uses of wgkey to the new key interfaces.
It now has specific machine, node and discovery keys and we now should
use them correctly.
Please note the new logic which strips a key prefix (in utils.go) that
is now standard inside tailscale.
In theory we could put it in the database, but to preserve backwards
compatibility and not spend a lot of resources on accounting for both,
we just strip them.
This commit adds a sentral cache to keep track of clients whom has
requested an expiry time, but were we need to keep hold of it until the
second request comes in.
We should never expose errors via web, it gives attackers a lot of info
(Insert OWASP guide).
Also handle error that didnt separate not found gorm issue and other
errors.
