You can now install from private registries and custom npm auth without any workarounds. Two optional fields are supported on POST https://www.node-modules-cache.com/api/v2/npm/ci:
.npmrc- raw.npmrctext, written into the project beforenpm ciruns.environmentVariables- an arbitrary string-to-string map made available during the install, so you can pass registry tokens and other configuration.
Reference a token as ${YOUR_TOKEN} in .npmrc and send its value in environmentVariables in the same request. Ideal for private scopes such as Font Awesome Pro. Both fields are part of the cache identity, so changing them produces a fresh cache entry.
See the implementation guide for full examples.