Log in with Privy token

Optional Solana wallet pubkey the caller is asserting ownership of. For first-time bindings ownership must be proved either by including wallet_proof (a Solana memo transaction signed by the wallet — works for Ledger which cannot sign off-chain messages) or, absent a proof, by Privy's linked_accounts API confirming the wallet is linked to the authenticated user. An unverified pubkey is rejected with wallet_not_linked. For returning users, if supplied, it must match the bound pubkey. If omitted when no mapping exists, login still succeeds but the issued token will not carry a wallet claim and so cannot satisfy user-scoped authorization.