OCSP Stapling

[wallyqs]

Adds basic OCSP Stapling support in the server for client connections. To enable, the server has to start with the following:

ocsp: true

tls { ... }

When OCSP is enabled this way, in case a certificate has a 'status_request' // Must Staple flag toggled, then it will make an
HTTP request to the OCSP remote url and fetch staples that will be cached on disk and serve the staples to the clients so that they can confirm the response. The TLS certificates can change at anytime and OCSP stapling is reloading aware.

To store OCSP Staples to disk, a store dir can be configured as follows:

store_dir = "./store-dir"

Or in case there is a store dir for JetStream that will be used instead:

jetstream {
  store_dir = "./store-dir"
}

The OCSP staples will be stored at a created directory underneath like $store_dir/ocsp.

/cc @nats-io/core

[philpennock]

I confess, I'm a little sad that we're not following the state.directory pattern. Ah well.

[ColinSullivan1]

LGTM.

[kozlovic]

LGTM