Also introduce caddy.OnProcessExit which is a list of functions that
run before exiting the process cleanly; these do not count as shutdown
callbacks, so they do not return errors and must execute quickly.

- Expose the list of Caddy instances through caddy.Instances()

- Added arbitrary storage to caddy.Instance

- The cache of loaded certificates is no longer global; now scoped
  per-instance, meaning upon reload (like SIGUSR1) the old cert cache
  will be discarded entirely, whereas before, aggressively reloading
  config that added and removed lots of sites would cause unnecessary
  build-up in the cache over time.

- Key certificates in the cache by their SHA-256 hash instead of
  by their names. This means certificates will not be duplicated in
  memory (within each instance), making Caddy much more memory-efficient
  for large-scale deployments with thousands of sites sharing certs.

- Perform name-to-certificate lookups scoped per caddytls.Config instead
  of a single global lookup. This prevents certificates from stepping on
  each other when they overlap in their names.

- Do not allow TLS configurations keyed by the same hostname to be
  different; this now throws an error.

- Updated relevant tests, with a stark awareness that more tests are
  needed.

- Change the NewContext function signature to include an *Instance.

- Strongly recommend (basically require) use of caddytls.NewConfig()
  to create a new *caddytls.Config, to ensure pointers to the instance
  certificate cache are initialized properly.

- Update the TLS-SNI challenge solver (even though TLS-SNI is disabled
  currently on the CA side). Store temporary challenge cert in instance
  cache, but do so directly by the ACME challenge name, not the hash.
  Modified the getCertificate function to check the cache directly for
  a name match if one isn't found otherwise. This will allow any
  caddytls.Config to be able to help solve a TLS-SNI challenge, with one
  extra side-effect that might actually be kind of interesting (and
  useless): clients could send a certificate's hash as the SNI and
  Caddy would be able to serve that certificate for the handshake.

- Do not attempt to match a "default" (random) certificate when SNI
  is present but unrecognized; return no certificate so a TLS alert
  happens instead.

- Store an Instance in the list of instances even while the instance
  is still starting up (this allows access to the cert cache for
  performing renewals at startup, etc). Will be removed from list again
  if instance startup fails.

- Laid groundwork for ACMEv2 and Let's Encrypt wildcard support.

Server type plugins will need to be updated slightly to accommodate
minor adjustments to their API (like passing in an Instance). This
commit includes the changes for the HTTP server.

Certain Caddyfile configurations might error out with this change, if
they configured different TLS settings for the same hostname.

This change trades some complexity for other complexity, but ultimately
this new complexity is more correct and robust than earlier logic.

Fixes #1991
Fixes #1994
Fixes #1303

* First working mask

* IP Mask working with defaults and empty

* add tests for ipmask

* Store Mask as setup, some tidying, cleaner flow

* Prevent mask from running when directive not present

* use custom replacement to store masked ip

Caddyfile snippets

This allows custom replacements to be defined in a way that propagates
throughout all plugins.

* Checking that a server listener is not nil before printing verbose information

* Improved readability of a loop

* Simplify parseUpstream function

* Add SRV support for proxy upstream

Signed-off-by: Tw <tw19881113@gmail.com>

This adds the ask sub-directive to tls that defines the URL of a backend HTTP service to be queried during the TLS handshake to determine if an on-demand TLS certificate should be acquired for incoming hostnames. When the ask sub-directive is defined, Caddy will query the URL for permission to acquire a cert by making a HTTP GET request to the URL including the requested domain in the query string. If the backend service returns a 2xx response Caddy will acquire a cert. Any other response code (including 3xx redirects) are be considered a rejection and the certificate will not be acquired.

* Update build instruction

This changes add proper an easy instruction for building.

* Update README.md

The rc.subr framework already takes care of substituting user. So, using
daemon's -u option is double user-substitution and fails if $caddy_user
is non-root.

caddy.go:569: could be simplified

sigtrap_posix.go:87: value of inst is never used

upgrade.go:151: should omit nil check; len() for nil slices is defined as zero

Changes the log output of on startup

* Handle the case of an OCSP responder certificate expiring before an OCSP response it issued

* oops

* doh, gofmt