To configure Yarn to use a custom NPM registry and enable authentication for the npm scope, use the following commands:

1. Set the NPM registry server for the npm scope:

   yarn config set npmScopes.npm.npmRegistryServer "https://registry.npmjs.org"

2. Always authenticate for the npm scope:

   yarn config set npmScopes.npm.npmAlwaysAuth true

3. Set the authentication token for the npm scope:

   yarn config set npmScopes.npm.npmAuthToken "YOUR_NPM_TOKEN"