The scrape config names a client_secret_file; this is what puts a file
there. A host oneshot copies authelia's minted secret between the two
container trees — a copy and not a bind mount, because the secret does
not exist until authelia's first boot and nixos-container refuses to
start on a missing bind source, which on a fresh swarm is a permanent
stall presenting as broken metrics.
The collector runs under DynamicUser and the prometheus receiver opens
client_secret_file itself, as that user, so there is no uid to hand the
file to. LoadCredential reads it as root before the sandbox exists and
re-exposes it under a path that does not depend on which uid the unit
got; the scrape config points there. Both spellings derive from one
binding, since a mismatch is a file the collector cannot open and
nothing but a runtime 401 would say so.
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