remake: turning a running swarm strict, keeping what an operator signed

Until a swarm is strict, the user a change names is its node's word, so
any member could have planted registry entries, policy, bans or
user-signed values as any user, plain or signed by a key it put there
itself; writing the strict policy trusted all of it as it was.

A remake of a new kind, `strict`, turns a swarm strict instead:

* Its content is a manifest (access::strict): the swarm, the strict
  policy, and each value kept at the places values are signed, by the
  SHA-256 of its JSON, signed by an operator (ssh-keygen -Y sign -n
  continuum-strict).
* Every node builds the next epoch as compaction does, keeping at the
  signed places only the values the manifest names, as they were at
  the base, and writing its policy (RemakeKind::protocol, the one kind
  that changes protocol data). Writes after the base reach the new
  epoch only by replays, judged by the strict policy.
* A node votes for one only with its manifest signed by one of
  --strict-keys, keys given out of the document; without any, for none
  (logged once, `Not voting for a strict remake`), unless
  --follow-strict-remakes. A coordinator proposes only what it would
  vote for (403). Once a majority commits one, every node switches, as
  with any remake: refusing to switch would only cut a node off.
* GET /admin/strict-manifest gives the manifest keeping everything held
  now, the values for review and the heads they are at;
  continuum-signed strict shows them, signs once confirmed and proposes
  at those heads.

The sim a_swarm_turning_strict_through_a_remake: a member plants a
registry entry as a manager; the operator's manifest leaves it out; a
and b, given the key, commit; c, without, follows; the entry is gone
and the policy strict everywhere.

1 files changed, 10 insertions, 0 deletions

diff --git a/docs/example.toml b/docs/example.toml
index cce8780..2c3a2ab 100644
--- a/docs/example.toml
+++ b/docs/example.toml
@@ -105,6 +105,16 @@ htpasswd = "/etc/continuum/htpasswd"
 # together at most.
 # key-logins-per-user = 100
 
+# SSH keys, as authorized_keys lines (ssh-ed25519 <base64> [comment]), whose signature
+# on a strict remake's manifest this node takes: the values kept when the swarm turns
+# strict (docs/access.md). Without, it votes for no strict remake, unless
+# follow-strict-remakes.
+# strict-keys = ["ssh-ed25519 AAAA… alice"]
+
+# Without strict-keys: vote for strict remakes all the same, taking the manifests as
+# the members proposing them sign them.
+# follow-strict-remakes = false
+
 # Where the reverse proxies whose user-header is believed connect from: IP addresses (or
 # ranges, as ADDRESS/BITS), and unix for the API's Unix sockets (bind-addr). On a host
 # with other users, leave out the addresses and have the proxy use a Unix socket: others