While it is possible to use systemd credentials via
LoadCredential=xyz.radicle.node.secret:…
ExecStart=radicle-node … --secret "${CREDENTIALS_DIRECTORY}/xyz.radicle.node.secret"
Make usage more convenient and directly support passing the secret key
via a systemd credential. The ID of the credential must be
xyz.radicle.node.secret
and is not user-configurable.
A systemd service unit file might contain:
LoadCredential=xyz.radicle.node.secret:…
ExecStart=radicle-node …
This requires just a bit of plumbing in `radicle-node`.
The preference order for the path of the secret key is:
1. The command line argument `--secret`.
2. The systemd credential.
3. The configuration file.
4. The default location to preserve backward compatibility.
The reason to prefer the systemd credential over the configuration file
is that it uses a mechanism that is influenced by the environment of the
process, which is deemed "closer at runtime" or "more dynamic" than a
configuration file. Ad-hoc overrides are still possible via the
commandline argument.
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