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docs: mention file placeholder for secrets #543

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12 changes: 12 additions & 0 deletions src/docs/markdown/caddyfile/concepts.md
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Expand Up @@ -821,4 +821,16 @@ For example, if you have the [`caddy-dns/cloudflare` plugin <img src="/old/resou
}
```

Environment variables are convenient, but sensitive values in a process environment can be exposed by process inspection, child process inheritance, logs, crash dumps, or platform diagnostics.

@francislavoie francislavoie Jun 29, 2026

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This line feels weird, because it's like "well everything you just read? forget about it because this and this and that." It's strange to have something criticize the use of env vars, in the env vars section of the docs (I don't disagree with the content though, it's true).

I don't have a specific answer to this, but it needs some rethinking of where exactly this fits into the docs.


For secrets, prefer your platform's secret management mechanism when available. If the secret is provided as a file, you can use the [global `{file.*}` placeholder](/docs/conventions#placeholders) in config fields which support placeholders:

```caddy
{
acme_dns cloudflare {file./run/secrets/cloudflare_api_token}
}
```

This does not make the secret inaccessible to Caddy; the Caddy process still needs permission to read the file. It avoids placing the secret value in the process-wide environment.

If you're running Caddy as a systemd service, see [these instructions](/docs/running#overrides) for setting service overrides to define your environment variables.

@francislavoie francislavoie Jun 29, 2026

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This section is still talking about env vars, so it's weird that the {file.*} stuff is cutting right in the middle of it. Needs reorganizing.

2 changes: 1 addition & 1 deletion src/docs/markdown/conventions.md
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Expand Up @@ -97,7 +97,7 @@ The following placeholders are always available (global):
Placeholder | Description
------------|-------------
`{env.*}` | Environment variable; example: `{env.HOME}`
`{file.*}` | Contents from a file; example: `{file./path/to/secret.txt}`
`{file.*}` | Contents from a file, useful when a secret is supplied as a file; example: `{file./path/to/secret.txt}`

@francislavoie francislavoie Jun 29, 2026

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I don't think this change is necessary, it's redundant - the example has secret.txt, pretty self explanatory.

I want to be careful on the length of the description mainly for visual reasons, line wrapping etc.

`{system.hostname}` | The system's local hostname
`{system.slash}` | The system's filepath separator
`{system.os}` | The system's OS
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