sign
Signs a transaction with the client domain signing key(s).
This delegate is called when client domain verification is required but the client domain signing key is not directly available (e.g., managed by HSM, custody service, or remote signing service).
For multi-signature threshold accounts, the delegate should add all required signatures to meet the account's signing threshold.
Return
Base64-encoded signed transaction envelope XDR with one or more client domain signatures added
Parameters
transaction
Base64-encoded transaction envelope XDR to sign