ClientDomainSigningDelegate

Functional interface for delegating client domain transaction signing to external services.

This delegate is for signing with your WALLET'S domain key to prove wallet identity during SEP-10 authentication. This is NOT for user account signing - use the signers parameter for that.

This enables integration with wallet backend infrastructure that manages the wallet's domain signing key:

• Wallet backend servers - Your company's authentication server managing the wallet's domain key

• Hardware Security Modules (HSMs) - Secure cryptographic key storage for wallet infrastructure

• Cloud KMS services - AWS KMS, Google Cloud KMS for wallet backend key management

• Multi-Party Computation (MPC) systems - Distributed key management for wallet infrastructure

Use Cases:

• Wallet backends where the domain signing key is managed server-side

• Enterprise wallet infrastructure requiring HSM-backed domain keys

• Wallet companies with regulatory requirements for key custody

• Multi-signature wallet domain accounts with threshold requirements

Multi-Signature Support:

• Wallet domain accounts can have multiple signers with threshold requirements

• The delegate can add multiple signatures to meet the wallet domain account's signing threshold

• Common for enterprise wallet backends where master key is disabled (weight = 0)

• Supports regulatory compliance requiring multi-custody signatures for wallet identity

Security Considerations:

• The delegate receives the full transaction XDR (not just a hash) for transparency

• Wallet backend can verify transaction contents before signing with domain key

• Returned transaction must not be modified (only signatures added)

• Network passphrase is embedded in transaction hash to prevent replay attacks

• Only use with your own trusted wallet backend services

Example - Wallet company HSM:

val signingDelegate = ClientDomainSigningDelegate { transactionXdr ->
    // Parse transaction
    val tx = AbstractTransaction.fromEnvelopeXdr(transactionXdr, network) as Transaction

    // Sign with your wallet company's HSM (not user's HSM)
    tx.sign(walletDomainHsmKeyPair)

    // Return signed transaction
    tx.toEnvelopeXdrBase64()
}

val token = webAuth.jwtToken(
    clientAccountId = userAccountId,
    signers = listOf(userKeyPair),
    clientDomain = "wallet.company.com",
    clientDomainSigningDelegate = signingDelegate
)

Example - Multi-signature wallet domain account:

val signingDelegate = ClientDomainSigningDelegate { transactionXdr ->
    val tx = AbstractTransaction.fromEnvelopeXdr(transactionXdr, network) as Transaction

    // Add multiple wallet domain signatures to meet threshold
    tx.sign(walletDomainSigner1KeyPair)
    tx.sign(walletDomainSigner2KeyPair)

    tx.toEnvelopeXdrBase64()
}

Example - Wallet backend server:

val signingDelegate = ClientDomainSigningDelegate { transactionXdr ->
    // Send to your wallet's backend server for domain signing
    val response = httpClient.post("https://backend.wallet-company.com/sign-client-domain") {
        contentType(ContentType.Application.Json)
        setBody("""{"transaction": "$transactionXdr"}""")
    }

    // Backend returns signed transaction
    response.body<String>()
}

See also