There is a Uservoice feature request for moderation to act the same way as subscriptions https://twitch.uservoice.com/forums/310213-developers/suggestions/39910141-copy-subscription-support-for-channel-moderation-s
Basically, for subscriptions because the channel explicitly chooses to allow/deny an extension access to their subscriber list, you can use an App Access Token (which you can generate without a website, or any action from the user) to get that list of subscribers on that channel. For moderation though there currently is no toggle for a streamer to grant your extension that same functionality, so going through the full authentication flow is currently the only way.
If you want to see that feature added you can vote for that suggestion linked, as Twitch use that site to determine what features have highly requested and if there are valid use cases for them to be developed.