Feat/add rpc header arg

[elizabethengelman]

What

Adds a --rpc-headers argument to allow users to pass in an auth header, so that RPC providers that require API keys can be used with the CLI.

Companion rpc-client PR: stellar/rs-stellar-rpc-client#13

Here are some screenshots showing that this change works for multiple headers, with both adding a new network, and using a configured rpc provider:

using multiple —rpc-headers args for adding a network

using env vars for multiple headers for adding a network

using multiple —rpc-headers args for using the rpc provider

using the env var for multiple headers for using the rpc provider

Why

This allows users to use one of the rpc providers that require an API passed in via a header.

Closes #1583

Known limitations

This change requires this change from the rpc-client: stellar/rs-stellar-rpc-client#13

[leighmcculloch]

Couple thoughts. I realise this PR is incomplete and doesn't yet use the header. 😅

[leighmcculloch]

Couple requests inline.

[leighmcculloch]

I think this is good 👍🏻. Thanks for navigating both the rpc and cli changes. I've merged the rpc change, and bumped the ref in this pr to match it so this should be good to merge.

@elizabethengelman a couple minor asks for a follow up:

1️⃣ The error messages when passing invalid values of keys / values to the header could do a better job of helping someone know what to correct.

For example, it's easy to naively think you can just plop in an api key:

$ stellar network add lfg --rpc-header myapikeyyay
error: invalid value 'myapikeyyay' for '--rpc-header <RPC_HEADERS>': invalid header: Missing header value: myapikeyyay

For more information, try '--help'.

I understand what the error above needs of me, but I think devs without context won't.

I think we should tell them that the header should be in the format key: value.

2️⃣ White space could be ignored.

For example, it's common for folks to state headers with whitespace around the ::

$ stellar network add lfg \
    --rpc-url http://example.org \
    --network-passphrase "Example Network" \
    --rpc-header 'Authorization: myapikeyyay'

Which renders later with the whitespace retained:

❯ stellar network ls -l
Local "/Users/lfg/.soroban/network/lfg.toml"
Name: lfg
Network {
    rpc_url: "http://example.org",
    rpc_headers: [
        (
            "Authorization",
            " myapikeyyay",
        ),
    ],
    network_passphrase: "Example Network",
}

[leighmcculloch]

@elizabethengelman while trying out the pr locally I made this tweak, I renamed the option --rpc-header (no plural) so that at the command line it's more obvious that using the option is intended to be a single arg per use, so it looks like this:

stellar ... --rpc-header A:B --rpc-header C:D

So that folks don't think they can do:

stellar ... --rpc-headers A:B C:D

It looked like you had --rpc-header in the help docs, so I think that was what you were intending to do in any case. Lmk if I misunderstood or if this doesn't fit with the overall plan here.

[leighmcculloch]

I pushed a change to trim values, and to tweak the error message. The error generated by this line looks like this now:

$ stellar network add lfg \
    --rpc-url http://example.org \
    --network-passphrase "Example Network" \
    --rpc-header 'Authorization'
error: invalid value 'Authorization' for '--rpc-header <RPC_HEADERS>': invalid HTTP header: must be in the form 'key:value'

I removed passing in the string into the error, because the clap error handler will print out the value they passed in at the start of the error message anyway.