feat(sdk-core): improve wallet.signTransaction to get the user key

In order to allow the signTssTx express endpoint to sign tx without external signer, we need to
modify the signTransaction method to get the key if the walletPassphrase is provided

WP-2535

TICKET: WP-2523

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

@@ -206,6 +206,7 @@ export interface WalletSignTransactionOptions extends WalletSignBaseOptions {
   customMPCv2SigningRound3GenerationFunction?: CustomMPCv2SigningRound3GeneratingFunction;
   apiVersion?: ApiVersion;
   multisigTypeVersion?: 'MPCv2';
+  walletPassphrase?: string;
   [index: string]: unknown;
 }
 

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

@@ -1717,6 +1717,21 @@ export class Wallet implements IWallet {
       params.txPrebuild = { txRequestId };
     }
 
+    if (params.walletPassphrase && !(params.keychain || params.key)) {
+      if (!_.isString(params.walletPassphrase)) {
+        throw new Error('walletPassphrase must be a string');
+      }
+      const keychains = await this.getKeychainsAndValidatePassphrase({
+        reqId: params.reqId,
+        walletPassphrase: params.walletPassphrase,
+      });
+      const userKeychain = keychains[0];
+      if (!userKeychain || !userKeychain.encryptedPrv) {
+        throw new Error('the user keychain does not have property encryptedPrv');
+      }
+      params.keychain = userKeychain;
+    }
+
     const presign = await this.baseCoin.presignTransaction({
       ...params,
       walletData: this._wallet,