Tailscale Caddy plugin

The Tailscale Caddy plugin brings Tailscale integration to the Caddy web server. It's really multiple plugins in one, providing:

• the ability for a Caddy server to directly join your Tailscale network without needing a separate Tailscale client.
• a Caddy authentication provider, so that you can pass a user's Tailscale identity to an applicatiton.
• a Caddy subcommand to quickly setup a reverse-proxy using either or both of the network listener or authentication provider.

This plugin is still very experimental.

Installation

Use xcaddy to build Caddy with the Tailscale plugin included.

xcaddy build master --with github.com/tailscale/caddy-tailscale

Caddy network listener

New in Caddy 2.6, modules are able to provide custom network listeners. This allows your Caddy server to directly join your Tailscale network without needing a separate Tailcale client running on the machine exposing a network device. Each site can be configured in Caddy to join your network as a separate node, or you can have multiple sites listening on different ports of a single node.

Configuration

Configure Caddy to listen on a special "tailscale" network address. If using a Caddyfile, use the bind directive:

:80 {
    bind tailscale/
}

You can also specify a hostname to use for the Tailscale node:

:80 {
    bind tailscale/myhost
}

If using the Caddy JSON configuration, specify a "tailscale/" network in your listen address:

{
  "apps": {
    "http": {
      "servers": {
        "srv0": {
          "listen": [
            "tailscale/myhost:80"
          ]
        }
      }
    }
  }
}

Caddy will join your Tailscale network and listen only on that network interface. Multiple addresses can be specified if you want to listen on the Tailscale address as well as a local address:

:80 {
  bind tailscale/myhost localhost
}

Different sites can be configured to join the network as different nodes:

:80 {
  bind tailscale/a
}

:80 {
  bind tailscale/b
}

However, having a single Caddy site connect to separate Tailscale nodes doesn't quite work correctly. If this is something you actually need, please open an issue.

HTTPS support

At this time, the Tailscale plugin for Caddy doesn't support using Caddy's native HTTPS resolvers. You will need to use the tailscale+tls bind protocol with a configuration like this:

{
    order tailscale_auth after basicauth
    auto_https off
}

:443 {
    bind tailscale+tls/myhost
}

Please note that because you currently need to turn auto_https support off, it is not advised to use the same instance of Caddy for your external-facing apps as you use for your internal-facing apps. This deficiency will be resolved as soon as possible.

Authenticating to the Tailcale network

New nodes can be added to your Tailscale network by providing an Auth key or by following a special URL. Auth keys are provided to Caddy via the TS_AUTHKEY or TS_AUTHKEY_<HOST> environment variable. So if your network listener was tailscale/myhost, then it would look first for the TS_AUTHKEY_MYHOST environment variable, then TS_AUTHKEY.

If no auth key is provided, then Tailscale will generate a URL that can be used to add the new node and print it to the Caddy log. Tailscale logs can be somewhat noisy so are turned off by default. Set TS_VERBOSE=1 to see the URL logged. After the node had been added to your network, you can restart Caddy without the debug flag.

Caddy authentication provider

Setup the Tailscale authentication provider with tailscale_auth directive. The provider will enforce that all requests are coming from a Tailscale user, as well as set various fields on the Caddy user object that can be passed to applications, similar to nginx-auth.

Set the order directive in your global options to instruct Caddy when to process tailscale_auth. For example, in a Caddyfile:

{
  order tailscale_auth after basicauth
}

:80 {
  tailscale_auth
}

The following fields are set on the Caddy user object:

• user.id: the Tailscale email-ish user ID
• user.tailscale_login: the username portion of the Tailscale user ID
• user.tailscale_user: same as user.id
• user.tailscale_name: the display name of the Tailscale user
• user.tailscale_profile_picture: the URL of the Tailscale user's profile picture
• user.tailscale_tailnet: the name of the Tailscale network the user is a member of

These can be mapped to HTTP headers passed to an application using something like the following in your Caddyfile:

header_up X-Webauth-User {http.auth.user.tailscale_login}
header_up X-Webauth-Email {http.auth.user.tailscale_user}
header_up X-Webauth-Name {http.auth.user.tailscale_name}

When used with a Tailscale listener (described above), that Tailscale connection is used to identify the remote user. Otherwise, the authentication provider will attempt to connect to the Tailscale daemon running on the local machine.

tailscale-proxy subcommand

The Tailscale Caddy plugin also includes a tailscale-proxy subcommand that sets up a simple reverse proxy that can optionally join your Tailscale network, and will enforce Tailscale authentication and map user values to HTTP headers.

For example:

xcaddy tailscale-proxy --from "tailscale/myhost:80" --to localhost:8000