Unable to set bearerToken when creating NPM proxy repo via REST API

Creating an NPM proxy repo via the REST API fails when setting a bearerToken as an authentication option. The following response is returned:

"id": "BearerTokenAuthenticationConfiguration.attributes[httpclient].authentication.bearerToken", 
"message": "must not be blank"

To reproduce, attempt to create an NPM proxy repo via the REST API (POST /v1/repositories/npm/proxy) and for the authentication payload, pass in:

"authentication": {
 "type": "bearerToken",
 "bearerToken": "test"
 }

Expected:

REST API should accept bearer token auth configuration and the API example payload should be updated to indicate how a bearer token can be correctly set.