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Tailscale Authentication for NGINX

April 27 2022
Xe Iaso
Xe Iaso

Previously on the Tailscale blog, I walked through how authentication works with Tailscale for Grafana and even for Minecraft. Today we’re going to take that basic concept and show how to extend it to services that you have proxied behind NGINX.

The Grafana/Minecraft authentication proxy trick works because we set up a whole new node on your tailnet to proxy traffic directly to Grafana or Minecraft. This does work, but there’s a nonzero setup cost every time you add a new service to the mix. If you have an existing NGINX configuration for all your internal services, it may be easier to just use NGINX to proxy access to everything.

I have created nginx-auth to implement the NGINX HTTP subrequest authentication protocol. You can use this to authenticate every request to your internal services and then decorate requests to them with the right HTTP headers.

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I have added nginx-auth to the Tailscale repositories for x86_64 Linux machines. To install it on an Ubuntu machine, run this command:

sudo apt-get update && sudo apt-get install tailscale-nginx-auth
At the time of writing, this autoinstall strategy isn’t supported on non-Debian/Ubuntu. You can work around this by going into a checkout of tailscale/tailscale and checking out cmd/nginx-auth’s documentation on how to build packages.

This will automatically download the nginx-auth tool and other metadata needed to run it in systemd.

Once it is installed, you need to activate it in systemd with the following command:

sudo systemctl enable --now tailscale.nginx-auth.socket

This uses systemd socket activation to automatically start the service when it is needed. This lets systemd dynamically activate tailscale.nginx-auth.service on-demand instead of having it always run. This also automatically restarts the service if it crashes.

NGINX configuration

Once the tailscale.nginx-auth service is set up in your system, you need to configure NGINX to use it. This works in the server block, meaning that you can set up separate authentication logic for services listening over Tailscale vs services listening to the internet.

Set up an internal route named /auth (you can change this path should you need to):

location /auth {

  proxy_pass http://unix:/run/tailscale.nginx-auth.sock;
  proxy_pass_request_body off;

  proxy_set_header Host $http_host;
  proxy_set_header Remote-Addr $remote_addr;
  proxy_set_header Remote-Port $remote_port;
  proxy_set_header Original-URI $request_uri;

And then in your location block that reverse proxies to your service, add this just before the proxy_pass instruction to use it:

auth_request /auth;
auth_request_set $auth_user $upstream_http_tailscale_user;
auth_request_set $auth_name $upstream_http_tailscale_name;
auth_request_set $auth_login $upstream_http_tailscale_login;
auth_request_set $auth_tailnet $upstream_http_tailscale_tailnet;
auth_request_set $auth_profile_picture $upstream_http_tailscale_profile_picture;

proxy_set_header X-Webauth-User "$auth_user";
proxy_set_header X-Webauth-Name "$auth_name";
proxy_set_header X-Webauth-Login "$auth_login";
proxy_set_header X-Webauth-Tailnet "$auth_tailnet";
proxy_set_header X-Webauth-Profile-Picture "$auth_profile_picture";

From here you can configure your applications to use the contents of X-Webauth-User or the other headers to use that for authentication logic. For a full list of options that are exposed in these response headers, check the documentation table which includes header names, example values and descriptions.

Security benefits

Overall the security benefits of doing this are similar to setting up a corporate SSO system. By moving authentication into the Tailscale level, you no longer need to handle authentication yourself. You don’t need to have internal tools maintain their own account systems with their own passwords. People connect to the server over Tailscale, and Tailscale already knows who they are.

This will give you a Single-Sign-On (SSO) experience without having the installation and maintenance overhead of setting up a new OAuth2 client, nor enduring the toil involved with getting administrative approval to try things out.

This proxy listens over a UNIX socket instead of a network-facing TCP socket. This makes it impossible to accidentally expose the proxy to the network. When you have the ability to, you should have your services listen over UNIX sockets like this. It allows you to use normal filesystem permissions to limit access to services instead of having to configure firewall rules.

Get in touch

Did you try this? How did you like it? Ping us on Twitter @Tailscale or let us know on the forum. If you want to check out the source code of this authentication sidecar, check it out on GitHub.

Many thanks to @zrail for pointing out this NGINX feature. Their examples helped guide the development of this service.

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