Verify transactions signatures and nonce

verifyTx.ts

          const signedTransactionSerialized =
            credentials?.signedTransactionSerialized;
          const pubkey = credentials?.pubkey;
          const nonce = req.body?.csrfToken;

          if (!(signedTransactionSerialized && pubkey && nonce)) {
            throw new Error("Missing required credentials.");
          }

          const transaction = Transaction.from(
            Buffer.from(signedTransactionSerialized, "hex")
          );

          if (!transaction.verifySignatures()) {
            throw new Error("Incorrect signature.");
          }

          const txNonce = transaction.instructions[0].data.toString();
          if (txNonce !== nonce) {
            throw new Error("Invalid nonce.");
          }
          
          // Generate JWT token or whatever you need to for the user to get in