PoA, it’s a very simplistic protocol, where instead of miners racing to find a solution to a difficult problem, authorized signers can at any time at their own discretion create new blocks.
The challenges revolve around how to control minting frequency, how to distribute minting load (and opportunity) between the various signers and how to dynamically adapt the list of signers.
A PoA scheme is based on the idea that blocks may only be minted by trusted signers. As such, every block (or header) that a client sees can be matched against the list of trusted signers. The challenge here is how to maintain a list of authorized signers that can change in time? The obvious answer (store it in an Ethereum contract) is also the wrong answer: fast, light and warp sync don’t have access to the state during syncing.
The protocol of maintaining the list of authorized signers must be fully contained in the block headers.
The protocol of maintaining the list of authorized signers must fit fully into the current data models.
