Add custom parameter to silent auth request with auth0.js

Following up on this thread: How to Modify Access Token with acts_as claim to imitate user impersonation - #5 by tyf

I’m able to manually construct a URL containing an impersonation query parameter that a custom Action checks and injects into the idToken. However, the auth0.js library doesn’t allow arbitrary parameters to be added (error: Object literal may only specify known properties). Can you recommend a way we can add that custom query parameter or do we need to construct the URL manually?