Config variables not being resolved in middleware.json in Loopback 3

Question

I'm unable to get the restApiRoot variable to resolve when using it in middleware.json. I'm using Loopback 3. Here's my setup:

config.json

{
  "restApiRoot": "/api"
}

middleware.json

  "auth": {
    "./middleware/order-auth": {
      "paths": [
        "${restApiRoot}/Orders"
      ]
    }
  },

If I replace ${restApiRoot} with /api then it works. I found this issue which sounds identical, but their resolution was to update loopback and loopback-boot back in 2016, and my versions are well beyond this. My middleware.json matches my version (3) docs.

Answer 1

I believe that loopback-boot performs variable substitution only when } is the last character. See the source code in lib/plugin-base.js (loopback-boot version 3.x):

var DYNAMIC_CONFIG_PARAM = /\$\{(\w+)\}$/;
function getConfigVariable(app, param, useEnvVars) {
  var configVariable = param;
  var match = configVariable.match(DYNAMIC_CONFIG_PARAM);
  // etc.