HIVE Keychain is really useful for adding functionality in a quick way, and I really like that doing so does not require the user to expose their key data to the app itself, as that functionality is handled directly in keychain (which the user is okay with/used to anyway.) Being able to reference the blockchain itself for future confirmation allows for unique scenarios where you don't have to "trust" the transactions since you know your system will be streaming/querying the blockchain itself for the transaction.

In regard to the active authority, you could always set the account up for escrow, which means the streamer would simply send you crypto with a specific memo/ID that is then designated for your bot to use for transactions. The benefit of this is you would create a user interface for the streamer to use which would allow them to control settings like maximum-transaction amount per day, transfer amount per interaction, time period of transactions (like if the streamer wanted to setup a giveaway period,) etc. From a security perspective, I don't think them sending you crypto and then trusting your bot's escrow system is any less secure then the active authority that was granted.

To use a reference, the Splinterlands card rental system uses escrow for transactions, where the rent money is collected from the user at time of rental agreement and send to the Splinterlands escrow account; which then sends each day's rental funds to the original card-holder.