code: function addAuthHeaders ({ 
    auth,
    bearerToken, 
    headers, 
    overrideHeaders=false, 
  }) {
    if (overrideHeaders) return
    if (bearerToken) return { 
      headers: { ...headers, Authorization: `Bearer ${ bearerToken }` } 
    }
    if (auth) {
      const username = auth.username || ''
      const password = auth.password || ''
      const encodedToken = Base64.btoa(`${ username }:${ password }`)
      return {
        headers: { ...headers, Authorization: `Basic ${ encodedToken }` }
      }
    }
  }
docs: Sets auth headers if necessary