`BAO_CLIENT_CERT` decides which certificate the TLS handshake presents. It is
not an identity: cert auth is a login, and a `bao kv` call without a token asks
its token helper for one instead — a `sh` neither unit carries on `path`.
Measured on this host, from `swarm-bao-matrix-token.service`:
swarm-bao did not return secret/swarm/matrix/registration-token
failed to get token helper: error expanding config path "":
exec: "sh": executable file not found in $PATH
So the first credential meant to travel through the store never has, and the
publisher added last week would not have either.
`-token-only` rather than a plain login: storing is the default, and it stores
through that same helper, so the obvious form reproduces the failure one line
further down. It is `-field=token -no-store`, which keeps the token on stdout
and out of the filesystem.
The two units degrade differently on purpose, and that is preserved. The matrix
fetch is `Wants=`-only and must not hold up the homeserver, so a refused login
reports why and keeps the token already in place. The publisher is
`Restart=on-failure`, where a store that cannot authenticate this host is worth
retrying and "published 0" would read as an ordinary quiet day.
`swarm-bao.nix` is untouched: it authenticates with the bootstrap token from a
file, which is a real identity and not a cert exchange. Its shape is where the
export idiom here comes from.
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