In EIP-255 , @karalabe proposes a PoA-scheme which reuses the current header-fields. The PoA-scheme has the following scheme to handle forks (caused by malicious minters or general latency):
If the number of authorized signers are N, and we allow each signer to mint 1 block out of K, then at any point in time N-K miners are allowed to mint. To avoid these racing for blocks, every signer would add a small random "offset" to the time it releases a new block. This ensures that small forks are rare, but occasionally still happen (as on the main net). If a signer is caught abusing it's authority and causing chaos, it can be voted out.
This gist outlines another scheme, by using the difficulty
header.