401 error on npm actions in newer npm client versions

In recent versions of npm (I'm using 6.9.0) the authentication token that is saved to the .npmrc file is incompatible with nexus, which makes the whole npm adduser command redundant.

so, if I do:

npm adduser --registry https://my.registry.com/

I get this added to my .npmrc

//my.registry.com/:_authToken=NpmToken.e33cd56f-ddac-3fcb-aae1-ac0c09e1d127

After this, any step that I perform fails with a HTTP 401, including the same adduser command or any install command.

The only way to correctly authenticate is the _auth base64 token detailed in https://support.sonatype.com/hc/en-us/articles/115015110067-Using-User-Token-s-with-NPM

Effectively, by not supporting these type of tokens, I believe that the bugfix from NEXUS-7989 has regressed.