Provably-Fair Verification
Every match outcome is committed before play via a hashed server seed. After the round the server seed is revealed — verify here that the result was fixed in advance and not altered.
How it works
Before the round we publish SHA-256(serverSeed). You pick your clientSeed. The outcome = HMAC-SHA256(serverSeed, clientSeed:nonce). Because the server committed to serverSeed via its hash beforehand, it could not change the result after seeing your seed.