Unable to publish to an NPM Registry (local)

As it turns out, I did not have the Npm Bearer Token Realm in my list of active realms. Once I moved it to Active, the publish completed successfully!

Additonally to @EdH's answer we discovered that the format of .npmrc has changed so base64 encoded _auth will not work anymore... and the token has to be created by logging into the repo.

old .npmrc

registry=https://host/repo
_auth=12afdjsljl123213

new .npmrc

//host/repo/:_authtoken=uuidOfToken