Function build_auth_token 

pub fn build_auth_token(
    deadline_unix_secs: i64,
    account_index: i64,
    api_key_index: u8,
    sk: &PrivateKey,
    k: Scalar,
) -> Result<SecretString, AuthTokenError>

Build a Lighter auth token using the system clock as the now reference.

Validates the deadline against LIGHTER_AUTH_TOKEN_MAX_TTL. See build_auth_token_at for an injectable-now variant suitable for tests.

Errors

Returns an error if deadline_unix_secs <= now, if it exceeds the venue cap, or if the system clock predates the UNIX epoch.