deploy: route frontend and core through one origin

docker/frontend-entrypoint.sh

@@ -1,15 +1,23 @@
 #!/bin/sh
 set -eu
 
-backend_base_url=${BACKEND_BASE_URL-/api}
-if ! /usr/local/bin/validate-backend-url "$backend_base_url"; then
-  echo "Invalid BACKEND_BASE_URL: use empty/root, /api, or a valid http(s) base without credentials, query, or fragment" >&2
+THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM:-http://core:8787}
+THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM%/}
+case "$THT_FRONTEND_API_UPSTREAM" in
+  http://*|https://*) ;;
+  *)
+    echo "Invalid THT_FRONTEND_API_UPSTREAM: use an internal http(s) upstream" >&2
+    exit 2
+    ;;
+esac
+export THT_FRONTEND_API_UPSTREAM
+
+if ! envsubst '${THT_FRONTEND_API_UPSTREAM}' \
+    < /etc/nginx/templates/default.conf.template \
+    > /etc/nginx/conf.d/default.conf; then
+  echo "Unable to render nginx API upstream configuration" >&2
   exit 2
 fi
-runtime_config=$(jq -cn --arg backend_base_url "$backend_base_url" \
-  '{backendBaseUrl: $backend_base_url}')
-printf 'window.__THOTHII_CONFIG__ = %s;\n' "$runtime_config" \
-  > /usr/share/nginx/html/config.js
 
 if [ "$#" -gt 0 ]; then
   exec "$@"