[infrastructure] Generate a session cookie encryption key on fresh self-hosted installs (#7056)

The community and enterprise bootstrap scripts now generate a dedicated
`server.auth.sessionCookieEncryptionKey` from 32 random bytes for fresh
installations.
The key is Base64-encoded, persisted independently from the datastore
encryption key, and reused from the generated configuration after
restarts.

The community script now also creates `config.yaml` with mode `0600`
before writing it, matching the existing enterprise behavior.

The server already supports the session cookie encryption key, but the
bootstrap scripts left it unset.
This adds defense-in-depth for newly generated deployments while
preserving the existing server-side nonce validation.
Because this only changes newly generated configuration, existing
installations and sessions are unchanged.

A focused regression test checks key presence, decoded length,
separation from the datastore key, YAML placement, and file mode for
both scripts.
It is included in the infrastructure workflow.

.github/workflows/test-infrastructure-files.yml

@@ -257,6 +257,15 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: Verify fresh-install session cookie key hardening
+        run: |
+          grep -Fxq '  SESSION_COOKIE_ENCRYPTION_KEY=$(openssl rand -base64 32)' infrastructure_files/getting-started.sh
+          grep -Fxq '    sessionCookieEncryptionKey: "$SESSION_COOKIE_ENCRYPTION_KEY"' infrastructure_files/getting-started.sh
+          grep -Fxq '  install -m 600 /dev/null config.yaml' infrastructure_files/getting-started.sh
+          grep -Fxq '  openssl rand -base64 32' infrastructure_files/getting-started-enterprise.sh
+          grep -Fxq '  NETBIRD_SESSION_COOKIE_ENCRYPTION_KEY=$(rand_b64_key)' infrastructure_files/getting-started-enterprise.sh
+          grep -Fxq '    sessionCookieEncryptionKey: "${NETBIRD_SESSION_COOKIE_ENCRYPTION_KEY}"' infrastructure_files/getting-started-enterprise.sh
+
       - name: Verify Dex retirement notice
         run: |
           if infrastructure_files/getting-started-with-dex.sh >stdout.txt 2>stderr.txt; then

infrastructure_files/getting-started-enterprise.sh

@@ -262,6 +262,7 @@ init_environment() {
   POSTGRES_DB="netbird"
   POSTGRES_PASSWORD=$(rand_secret)
   NETBIRD_ENCRYPTION_KEY=$(rand_b64_key)
+  NETBIRD_SESSION_COOKIE_ENCRYPTION_KEY=$(rand_b64_key)
   NETBIRD_RELAY_AUTH_SECRET=$(rand_secret)
 
   POSTGRES_DSN="host=postgres user=${POSTGRES_USER} password=${POSTGRES_PASSWORD} dbname=${POSTGRES_DB} port=5432 sslmode=disable TimeZone=UTC"
@@ -696,6 +697,7 @@ server:
     issuer: "https://${NETBIRD_DOMAIN}/oauth2"
     localAuthDisabled: false
     signKeyRefreshEnabled: false
+    sessionCookieEncryptionKey: "${NETBIRD_SESSION_COOKIE_ENCRYPTION_KEY}"
     dashboardRedirectURIs:
       - "https://${NETBIRD_DOMAIN}/nb-auth"
       - "https://${NETBIRD_DOMAIN}/nb-silent-auth"

infrastructure_files/getting-started.sh

@@ -348,6 +348,7 @@ initialize_default_values() {
   NETBIRD_RELAY_AUTH_SECRET=$(openssl rand -base64 32 | sed "$SED_STRIP_PADDING")
   # Note: DataStoreEncryptionKey must keep base64 padding (=) for Go's base64.StdEncoding
   DATASTORE_ENCRYPTION_KEY=$(openssl rand -base64 32)
+  SESSION_COOKIE_ENCRYPTION_KEY=$(openssl rand -base64 32)
   NETBIRD_STUN_PORT=3478
 
   # Docker images
@@ -527,7 +528,8 @@ generate_configuration_files() {
 
   # Common files for all configurations
   render_dashboard_env > dashboard.env
-  render_combined_yaml > config.yaml
+  install -m 600 /dev/null config.yaml
+  render_combined_yaml >> config.yaml
   return 0
 }
 
@@ -911,6 +913,7 @@ server:
   auth:
     issuer: "$NETBIRD_HTTP_PROTOCOL://$NETBIRD_DOMAIN/oauth2"
     signKeyRefreshEnabled: true
+    sessionCookieEncryptionKey: "$SESSION_COOKIE_ENCRYPTION_KEY"
     dashboardRedirectURIs:
       - "$NETBIRD_HTTP_PROTOCOL://$NETBIRD_DOMAIN/nb-auth"
       - "$NETBIRD_HTTP_PROTOCOL://$NETBIRD_DOMAIN/nb-silent-auth"