tailscale: add support for auth key secrets

README.md

@@ -16,14 +16,29 @@ to your `devcontainer.json`:
 }
 ```
 
-Then launch your Codespace. After it starts up, run [`tailscale up`](https://tailscale.com/kb/1080/cli/#up):
+## Starting Tailscale
+
+The Tailscale daemon starts automatically as part of the devcontainer entrypoint.
+
+### Manual Log in
 
 ```shell
 sudo tailscale up --accept-routes
 ```
 
-You'll only need to run `tailscale up` once per Codespace.
-The Tailscale state will be saved between rebuilds.
+More info: [`tailscale up`](https://tailscale.com/kb/1080/cli/#up)
+
+### Automatic login
+
+Create an [auth key](https://tailscale.com/kb/1085/auth-keys) in the Tailscale
+[admin panel](https://login.tailscale.com/admin/settings/keys).
+
+Create a codespace secret called `TS_AUTH_KEY` in your
+[codespaces configuration](https://github.com/settings/codespaces) containing
+the auth key you made above.
+
+Now whenever you launch a devcontainer with access to this secret, it will
+automatically perform a `tailscale up --accept-routes --auth-key=$TS_AUTH_KEY`.
 
 ## Details
 

src/tailscale/tailscaled-devcontainer-start.sh

@@ -11,6 +11,11 @@ if [[ $(id -u) -ne 0 ]]; then
   exec sudo --non-interactive -E "$0" "$@"
 fi
 
+# Move the auth key to a non-exported variable so it is not leaking into child
+# process environments.
+auth_key="$TS_AUTH_KEY"
+unset TS_AUTH_KEY
+
 if [[ ! -c /dev/net/tun ]]; then
   mkdir -p /dev/net
   mknod /dev/net/tun c 10 200
@@ -31,11 +36,18 @@ TAILSCALED_PID=""
 TAILSCALED_SOCK=/var/run/tailscale/tailscaled.sock
 TAILSCALED_LOG=/var/log/tailscaled.log
 
-# Note: TS_DEBUG_FIREWALL_MODE: it is not recommended that users copy this
-# setting into other environments, the feature is in test and will be formally
-# released in the future, debug flags may later be recycled for other purposes
-# leading to unexpected behavior.
->$TAILSCALED_LOG 2>&1 TS_DEBUG_FIREWALL_MODE=auto /usr/local/sbin/tailscaled &
+(
+  exec 1>$TAILSCALED_LOG 2>&1
+  cd /
+  umask 0
+  # Note: TS_DEBUG_FIREWALL_MODE: it is not recommended that users copy this
+  # setting into other environments, the feature is in test and will be formally
+  # released in the future, debug flags may later be recycled for other purposes
+  # leading to unexpected behavior.
+  unset TAILSCALED_PID TAILSCALED_SOCK TAILSCALED_LOG
+  export TS_DEBUG_FIREWALL_MODE=auto
+  exec setsid /usr/local/sbin/tailscaled
+) &
 TAILSCALED_PID=$!
 
 if [[ -n "$TAILSCALED_PID" ]]; then
@@ -50,4 +62,16 @@ if [[ -n "$TAILSCALED_PID" ]]; then
       break
     fi
   done
+fi
+
+if [[ -n "$auth_key" ]]; then
+  if [[ "$auth_key" == "test-auth-key" ]]; then
+    touch /tmp/test-auth-key-seen
+  else
+    hostnamearg=""
+    if [[ -n "${CODESPACE_NAME}" ]]; then
+      hostnamearg="--hostname=${CODESPACE_NAME}"
+    fi
+    /usr/local/sbin/tailscale up --accept-routes --authkey="$auth_key" $hostnamearg
+  fi
 fi

src/tailscale/tailscaled-entrypoint.sh

@@ -5,4 +5,6 @@
 
 /usr/local/sbin/tailscaled-devcontainer-start
 
+unset TS_AUTH_KEY
+
 exec "$@"

test/tailscale/scenarios.json

@@ -18,5 +18,14 @@
                 "version": "1.80.2"
             }
         }
+    },
+    "tailscale_auth_key": {
+        "image": "ubuntu:latest",
+        "containerEnv": {
+            "TS_AUTH_KEY": "test-auth-key"
+        },
+        "features": {
+            "tailscale": {}
+        }
     }
 }

test/tailscale/tailscale_auth_key.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Copyright (c) 2025 Tailscale Inc & AUTHORS All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+set -e
+
+source dev-container-features-test-lib
+
+# Wait for the auth key to be seen by the start script.
+count=100
+while ((count--)); do
+    [[ -f /tmp/test-auth-key-seen ]] && break
+    sleep 0.1
+done
+
+check "/tmp/test-auth-key-seen" ls /tmp/test-auth-key-seen
+
+# It would be nice to directly test that the entrypoint is doing unset
+# TS_AUTH_KEY, however that isn't visible to the test execution.
+
+reportResults

test/tailscale/test.sh

@@ -7,10 +7,10 @@ set -e
 
 source dev-container-features-test-lib
 
-if [[ "$VERSION" == latest ]]; then
-    check "Daemon: " tailscale version --daemon
-else
-    check "$VERSION" tailscale version --daemon
+check "daemon is running" tailscale version --daemon
+
+if [[ -n "$VERSION" ]]; then
+    check "version is correct" bash -c "tailscale version --daemon | grep -q $VERSION"
 fi
 
 reportResults