feat: implement BitGo signing in SDK

modules/express/src/clientRoutes.ts

@@ -403,6 +403,15 @@ function getWalletPwFromEnv(walletId: string): string {
   return walletPw;
 }
 
+/**
+ * Returns the wallet passphrase from the environment, or undefined if not set.
+ * Unlike getWalletPwFromEnv, this does not throw when the env variable is absent.
+ * Use this when the passphrase is optional (e.g. KMS-backed wallets).
+ */
+function findWalletPwFromEnv(walletId: string): string | undefined {
+  return process.env[`WALLET_${walletId}_PASSPHRASE`];
+}
+
 async function getEncryptedPrivKey(path: string, walletId: string): Promise<string> {
   const privKeyFile = await fs.readFile(path, { encoding: 'utf8' });
   const encryptedPrivKey = JSON.parse(privKeyFile);
@@ -629,7 +638,9 @@ export async function handleV2OFCSignPayload(
     throw new ApiResponseError(`Could not find OFC wallet ${walletId}`, 404);
   }
 
-  const walletPassphrase = bodyWalletPassphrase || getWalletPwFromEnv(wallet.id());
+  // Prefer the passphrase from the request body; fall back to the env var.
+  // If neither is present, pass undefined — signPayload() routes to KMS internally.
+  const walletPassphrase = bodyWalletPassphrase ?? findWalletPwFromEnv(wallet.id());
   const tradingAccount = wallet.toTradingAccount();
   const stringifiedPayload = typeof payload === 'string' ? payload : JSON.stringify(payload);
   const signature = await tradingAccount.signPayload({

modules/express/test/unit/typedRoutes/ofcSignPayload.ts

@@ -223,10 +223,103 @@ describe('OfcSignPayload codec tests', function () {
       const decodedResponse = assertDecode(OfcSignPayloadResponse200, result.body);
       assert.strictEqual(decodedResponse.signature, mockSignPayloadResponse.signature);
 
+      // Verify env passphrase was forwarded to signPayload
+      const signCall = mockTradingAccount.signPayload.getCall(0);
+      assert.ok(signCall, 'tradingAccount.signPayload should have been called');
+      assert.strictEqual(signCall.args[0].walletPassphrase, 'env_passphrase', 'env passphrase should be forwarded');
+
       // Cleanup environment variable
       delete process.env['WALLET_ofc-wallet-id-123_PASSPHRASE'];
     });
 
+    it('should pass undefined walletPassphrase to signPayload when no passphrase in body or env (KMS path)', async function () {
+      const requestBody = {
+        walletId: 'ofc-wallet-id-no-passphrase',
+        payload: { amount: '1000000', currency: 'USD' },
+        // no walletPassphrase
+      };
+
+      // Ensure no env var is set for this wallet
+      delete process.env['WALLET_ofc-wallet-id-no-passphrase_PASSPHRASE'];
+
+      const mockTradingAccount = {
+        signPayload: sinon.stub().resolves(mockSignPayloadResponse.signature),
+      };
+
+      const mockWallet = {
+        id: () => requestBody.walletId,
+        toTradingAccount: sinon.stub().returns(mockTradingAccount),
+      };
+
+      const walletsGetStub = sinon.stub().resolves(mockWallet);
+      const mockWallets = { get: walletsGetStub };
+      const mockCoin = { wallets: sinon.stub().returns(mockWallets) };
+      sinon.stub(BitGo.prototype, 'coin').returns(mockCoin as any);
+
+      const result = await agent
+        .post('/api/v2/ofc/signPayload')
+        .set('Authorization', 'Bearer test_access_token_12345')
+        .set('Content-Type', 'application/json')
+        .send(requestBody);
+
+      assert.strictEqual(result.status, 200);
+      const decodedResponse = assertDecode(OfcSignPayloadResponse200, result.body);
+      assert.strictEqual(decodedResponse.signature, mockSignPayloadResponse.signature);
+
+      // signPayload must be called with walletPassphrase=undefined so the SDK routes to KMS
+      const signCall = mockTradingAccount.signPayload.getCall(0);
+      assert.ok(signCall, 'tradingAccount.signPayload should have been called');
+      assert.strictEqual(
+        signCall.args[0].walletPassphrase,
+        undefined,
+        'walletPassphrase should be undefined to trigger KMS signing'
+      );
+    });
+
+    it('should prefer body walletPassphrase over env passphrase', async function () {
+      const requestBody = {
+        walletId: 'ofc-wallet-id-123',
+        payload: { amount: '500' },
+        walletPassphrase: 'body_passphrase',
+      };
+
+      // Set a different env passphrase — body should win
+      process.env['WALLET_ofc-wallet-id-123_PASSPHRASE'] = 'env_passphrase';
+
+      const mockTradingAccount = {
+        signPayload: sinon.stub().resolves(mockSignPayloadResponse.signature),
+      };
+
+      const mockWallet = {
+        id: () => requestBody.walletId,
+        toTradingAccount: sinon.stub().returns(mockTradingAccount),
+      };
+
+      const walletsGetStub = sinon.stub().resolves(mockWallet);
+      const mockWallets = { get: walletsGetStub };
+      const mockCoin = { wallets: sinon.stub().returns(mockWallets) };
+      sinon.stub(BitGo.prototype, 'coin').returns(mockCoin as any);
+
+      const result = await agent
+        .post('/api/v2/ofc/signPayload')
+        .set('Authorization', 'Bearer test_access_token_12345')
+        .set('Content-Type', 'application/json')
+        .send(requestBody);
+
+      assert.strictEqual(result.status, 200);
+
+      // body passphrase should take precedence
+      const signCall = mockTradingAccount.signPayload.getCall(0);
+      assert.ok(signCall, 'tradingAccount.signPayload should have been called');
+      assert.strictEqual(
+        signCall.args[0].walletPassphrase,
+        'body_passphrase',
+        'body passphrase should take precedence over env'
+      );
+
+      delete process.env['WALLET_ofc-wallet-id-123_PASSPHRASE'];
+    });
+
     it('should successfully sign complex nested JSON payload', async function () {
       const requestBody = {
         walletId: 'ofc-wallet-id-123',

modules/sdk-core/src/bitgo/trading/iTradingAccount.ts

@@ -2,7 +2,7 @@ import { ITradingNetwork } from './network';
 
 export interface SignPayloadParameters {
   payload: string | Record<string, unknown>;
-  walletPassphrase: string;
+  walletPassphrase?: string;
 }
 
 export interface ITradingAccount {

modules/sdk-core/src/bitgo/trading/tradingAccount.ts

@@ -23,13 +23,47 @@ export class TradingAccount implements ITradingAccount {
   }
 
   /**
-   * Signs an arbitrary payload with the user key on this trading account
+   * Signs an arbitrary payload. Use the user key if passphrase is provided, or the BitGo key if not.
    * @param params
    * @param params.payload arbitrary payload object (string | Record<string, unknown>)
    * @param params.walletPassphrase passphrase on this trading account, used to unlock the account user key
    * @returns hex-encoded signature of the payload
    */
   async signPayload(params: SignPayloadParameters): Promise<string> {
+    // if no passphrase is provided, attempt to sign using the wallet's bitgo key remotely
+    if (!params.walletPassphrase) {
+      return this.signPayloadByBitGoKey(params);
+    }
+    // if a passphrase is provided, we must be trying to sign using the user private key - decrypt and sign locally
+    return this.signPayloadByUserKey(params);
+  }
+
+  /**
+   * Signs the payload of a trading account via the trading account BitGo key stored in a remote KMS
+   * @param params
+   * @private
+   */
+  private async signPayloadByBitGoKey(params: Omit<SignPayloadParameters, 'walletPassphrase'>): Promise<string> {
+    const walletData = this.wallet.toJSON();
+    if (walletData.userKeySigningRequired) {
+      throw new Error('Wallet must use user key to sign ofc transaction, please provide the wallet passphrase');
+    }
+    if (walletData.keys.length < 2) {
+      throw new Error('Wallet does not support BitGo signing');
+    }
+
+    const url = this.wallet.url('/tx/sign');
+    const { signature } = await this.wallet.bitgo.post(url).send(params.payload).result();
+
+    return signature;
+  }
+
+  /**
+   * Signs the payload of a trading account locally by fetching the user's encrypted private key and decrypt using passphrase
+   * @param params
+   * @private
+   */
+  private async signPayloadByUserKey(params: SignPayloadParameters): Promise<string> {
     const key = (await this.wallet.baseCoin.keychains().get({ id: this.wallet.keyIds()[0] })) as any;
     const prv = this.wallet.bitgo.decrypt({
       input: key.encryptedPrv,

modules/sdk-core/src/bitgo/wallet/iWallet.ts

@@ -909,6 +909,7 @@ export interface WalletData {
   evmKeyRingReferenceWalletId?: string;
   isParent?: boolean;
   enabledChildChains?: string[];
+  userKeySigningRequired?: string;
 }
 
 export interface RecoverTokenOptions {

modules/sdk-core/src/coins/ofc.ts

@@ -15,6 +15,7 @@ import {
   SignTransactionOptions,
   VerifyAddressOptions,
   VerifyTransactionOptions,
+  Wallet,
 } from '../';
 
 export class Ofc extends BaseCoin {
@@ -104,6 +105,26 @@ export class Ofc extends BaseCoin {
     throw new MethodNotImplementedError();
   }
 
+  /**
+   * Signs a message using a trading wallet's BitGo Key
+   * @param wallet - uses the BitGo key of this trading wallet to sign the message remotely in a KMS
+   * @param message
+   */
+  async signMessage(wallet: Wallet, message: string): Promise<Buffer>;
+  /**
+   * Signs a message using the private key
+   * @param key - uses the private key to sign the message
+   * @param message
+   */
+  async signMessage(key: { prv: string }, message: string): Promise<Buffer>;
+  async signMessage(keyOrWallet: { prv: string } | Wallet, message: string): Promise<Buffer> {
+    if (!(keyOrWallet instanceof Wallet)) {
+      return super.signMessage(keyOrWallet as { prv: string }, message);
+    }
+    const signatureHexString = await (keyOrWallet as Wallet).toTradingAccount().signPayload({ payload: message });
+    return Buffer.from(signatureHexString, 'hex');
+  }
+
   /** @inheritDoc */
   auditDecryptedKey(params: AuditDecryptedKeyParams) {
     throw new MethodNotImplementedError();

modules/sdk-core/src/coins/ofcToken.ts

@@ -9,6 +9,7 @@ import {
   SignTransactionOptions as BaseSignTransactionOptions,
   SignedTransaction,
   ITransactionRecipient,
+  Wallet,
 } from '../';
 import { isBolt11Invoice } from '../lightning';
 
@@ -18,7 +19,8 @@ export interface SignTransactionOptions extends BaseSignTransactionOptions {
   txPrebuild: {
     payload: string;
   };
-  prv: string;
+  prv?: string;
+  wallet?: Wallet;
 }
 
 export { OfcTokenConfig };
@@ -107,15 +109,25 @@ export class OfcToken extends Ofc {
   }
 
   /**
-   * Assemble keychain and half-sign prebuilt transaction
+   * Signs a half-signed OFC transaction.
+   * Signs the transaction remotely using the BitGo key if prv is not provided.
    * @param params
    * @returns {Promise<SignedTransaction>}
    */
   async signTransaction(params: SignTransactionOptions): Promise<SignedTransaction> {
     const txPrebuild = params.txPrebuild;
     const payload = txPrebuild.payload;
-    const signatureBuffer = (await this.signMessage(params, payload)) as any;
-    const signature: string = signatureBuffer.toString('hex');
+
+    let signature: string;
+    if (params.wallet) {
+      signature = await params.wallet.toTradingAccount().signPayload({ payload, walletPassphrase: params.prv });
+    } else if (params.prv) {
+      const signatureBuffer = (await this.signMessage({ prv: params.prv }, payload)) as any;
+      signature = signatureBuffer.toString('hex');
+    } else {
+      throw new Error('You must pass in either one of wallet or prv');
+    }
+
     return { halfSigned: { payload, signature } } as any;
   }