caddyfile: Fix import replacing unrelated placeholders

[francislavoie]

See https://caddy.community/t/snippet-issue-works-outside-snippet/12231

So it turns out that NewReplacer() gives a replacer with some global defaults (like {env.*} and some system and time placeholders), which is not ideal when running import because we just want to replace {args.*} only, and nothing else.

[francislavoie]

I should probably add a test for this, but it can be merged without. It's on my TODO.

[mholt]

Interesting. Thanks for the patch. Can't think of a better way to do it, so let's roll with it.

[Dulanic]

Not sure that this corrected it. It is passing the env variable name not the env variable value. I looked at the autosave.json and all the other env variables show the value, but this same one just shows the name instead.

[francislavoie]

That's working as intended. The {env.*} are replaced at runtime, and only if the module being configured passes it through the replacer. The {$ENV} style are replaced at Caddyfile adapt time, i.e. before it's transformed into JSON, and will work anywhere, but will leak the values to the autosave.json

[francislavoie]

FYI @greenpau make sure you're running the replacer on all config values that are relevant either during ServeHTTP (if it makes sense for the value to be dynamic) or during Provision (if it only makes sense to be a single value for the lifetime of the server).

[Dulanic]

OK, I'll work /w @greenpau under his issue ticket since I'm still seeing errors. https://github.com/greenpau/caddy-auth-portal/issues/122#issuecomment-828481342