The receiving half authenticates per hive, so this half has to prove which
hive it is. It mints a token against the swarm's authelia with this hive's
client and posts to that hive's path on the collector's gateway name.
Holding a credential is what decides whether this tier authenticates —
`clientSecretFile` non-null — rather than a second switch that could
disagree with it. The default is the secret this host's own authelia
minted, which is right exactly when the IdP runs here; a hive that is not
that host names wherever the file landed, the same manual-copy shape the
identities option already documents as unsolved.
Two things that a diff will not explain:
`endpoint_params.audience` is not redundant with the client's registered
audience. Registering only makes an audience permissible; a token minted
without asking for one carries `aud: []` and every receiver refuses it,
with a config that reads correctly at both ends.
`client_secret_file` keeps the secret out of nix altogether — the
collector opens the file itself. It is a real key of this extension,
checked against the shipped binary with a deliberate typo rejected in the
same run, so "accepted" is distinguishable from "ignores everything". The
path comes from systemd's `CREDENTIALS_DIRECTORY`, so nothing hardcodes a
`/run/credentials` layout.
An assertion covers the one deployment where this can go wrong silently:
a host running both tiers with ingest authenticated and no credential to
present would 401 against a collector on the same machine.
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