Support setting request headers for reverse-proxy command

[damnever]

The one-line reverse-proxy command could be even better if it supports basic authentication like this:

caddy reverse-proxy --from :10000 --to http://user:pass@:20000

[francislavoie]

At that point, I'd argue you're better off using a Caddyfile and using header_up Authorization to set the credentials (base64 encode it ahead of time).

[damnever]

In my case, the one-line command is for temporary use in a safe environment.

[francislavoie]

The problem is --to is an upstream address (host+port, with scheme just as a hint to the transport options), not a URL. So using URL semantics like authentication is not supported in general. I don't think the added complexity is warranted, because we'd have to change our upstream address parsing code. See https://caddyserver.com/docs/caddyfile/directives/reverse_proxy#upstream-addresses for valid upstream addresses.

[damnever]

Another method is to add a command line option.

I am using caddy run -config - to work around this:

docker run --rm -p 10000:10000 library/caddy sh -c 'echo -e ":10000 {\n reverse_proxy :20000 {\n header_up Authorization \"Basic base64_encoded\"\n }\n}" | caddy run --adapter caddyfile --config -'

But this requires some extra effort to encode the credentials.

[mholt]

I'm also inclined to suggest a config file is the best answer here; but would a command line flag to set upgoing headers work for you?

[francislavoie]

I'd say a --header-up "<field>: <value>" option would be the way to go here. Maybe simply --header because it's probably very rare to need to set response headers in this case, and --response-header could be used for that later on if necessary.

[damnever]

An option to set headers sounds good to me.

[mholt]

--header-up is probably best (specific and consistent).

[francislavoie]

This will sorta depend on the work from #5379 otherwise we'd waste a bit of time setting up the type to accept multiple header values. With the cobra changes, we can just use StringSliceP() which is simpler.