How to set _auth for a scoped registry in .npmrc?

for some strange reason the _auth is called _authToken when used with scoped packages. If you are using this you don't have to store your plain text password in your .npmrc

registry=https://registry.npmjs.org/
@test-scope:registry=http://nexus:8081/nexus/content/repositories/npm-test/ 
//nexus:8081/nexus/content/repositories/npm-test/:_authToken=...
email=…

So, after some digging through the NPM source code, it turns out there is a way to do this.

My solution is below:

registry=https://registry.npmjs.org/
@test-scope:registry=http://nexus:8081/nexus/content/repositories/npm-test/
//nexus:8081/nexus/content/repositories/npm-test/:username=admin
//nexus:8081/nexus/content/repositories/npm-test/:_password=YWRtaW4xMjM=
email=…

Explanation:

The scope @test-scope specifies that packages with the scope should be published to a different registry than the default registry= when executing the npm publish command.

The two lines starting with //nexus:8081/... are used to specify the credentials to the scoped repository for both username and _password where _password is the base64 encoded password component from the previously used _auth credentials.

Using this approach, only scoped packages will be published and installed from the private registry and all other packages will be installed from the default registry.

Edit:

Additional to this, the password can be specified as an environment variable so that it is not stored in plaintext in the file.

For example:

registry=https://registry.npmjs.org/
@test-scope:registry=http://nexus:8081/nexus/content/repositories/npm-test/
//nexus:8081/nexus/content/repositories/npm-test/:username=admin
//nexus:8081/nexus/content/repositories/npm-test/:_password=${BASE64_PASSWORD}
email=…

Also, when using Nexus, the email= line must be specified.