Log in with signed wallet transaction

Echo of the nonce_id returned from the challenge endpoint.

Base64-encoded fully-signed Solana legacy transaction (bincode wire format). Must be the challenge transaction signed by wallet_pubkey. Wallets are permitted to include additional ComputeBudget or Lighthouse instructions before signing (in any position); any other instruction (other than the Memo issued by the server) is rejected. The server verifies the signature, the memo payload, and that the message still uses the issued blockhash so the signed bytes are never broadcastable on-chain.