`swarm-bao.nix` declared the store's half of the mTLS pair as options —
`serverCertFile`, `serverKeyFile`, `clientCaFile` — and left the reader's
half as a literal inside `glue-bao-tls.nix`, which only runs where
`deploy.bao.enable` is set. A hive that did not host the store therefore
could not read from it and could not be pointed at a certificate even
when one had been placed by hand.
Adds `clientCertFile`, `clientKeyFile` and `serverCaFile` beside their
three server siblings, `mkDefault`ed by the glue to the leaf it already
mints, and moves `glue-matrix-bao-token.nix` onto them. Its gate becomes
"this host holds an identity" rather than "the store is a neighbour",
and the unit ordering that names store-local units is now conditional --
`Requires=` on an absent unit fails the job.
`serverCaFile` is separate from `clientCaFile` on purpose: one is the
store choosing which readers to trust, the other a reader choosing which
store to trust. Self-signing collapses them to one file, which is a
property of that deployment and not of the pairing.
Closes#3855.
A CA that signs exactly two things -- the store's server certificate and
the client certificate of whoever reads from it -- and distributes
nothing. Not the hive CA, not the swarm CA: the store will distribute
both, and an authority you must already hold a certificate from cannot
be one the store hands out. Not the gateway's HTTPS material either,
self-signed or ACME; that is a different trust domain with a different
audience.
The minting lives here rather than in swarm-bao.nix because it is an
opinion about where the store's identity comes from -- the most
consequential one available. The service serves what it is handed. A
deployment with a real internal CA drops this file and names its own
paths in serverCertFile / clientCaFile, and nothing in the store
changes. Ordering simplifies too: with the unit and its consumer in one
module, before/requiredBy is internal rather than a cross-module fact.
Idempotent on ABSENCE only. Re-issuing the CA invalidates every client
certificate already trusting it, so a rebuild that refreshed it would
lock out every reader in the swarm at once.
