This enables ocsp-responder to talk to the RA and request freshly signed
OCSP responses.
ocsp/responder/redis_source is moved to ocsp/responder/redis/redis_source.go
and significantly modified. Instead of assuming a response is always available
in Redis, it wraps a live-signing source. When a response is not available,
it attempts a live signing.
If live signing succeeds, the Redis responder returns the result right away
and attempts to write a copy to Redis on a goroutine using a background
context.
To make things more efficient, I eliminate an unneeded ocsp.ParseResponse
from the storage path. And I factored out a FakeResponse helper to make
the unittests more manageable.
Commits should be reviewable one-by-one.
Fixes#6191
29724cb0b7