Using a custom signer gives "code": -32602, "message": "invalid 1st argument: userOperation invalid user operation fields"

[ebaizel]

I am creating a custom signer (code is below) that uses an AWS KMS key to sign User Operations. When I submit a UserOperation I get an error saying "code": -32602, "message": "invalid 1st argument: userOperation invalid user operation fields". I am using v3 of the Alchemy AA SDKs.

Here is the custom signer:

class SimpleKMSAccountSigner implements SmartAccountSigner {

  // key_id and sub are used to identify the user and their associated KMS key
  private key_id: string;
  private sub: string;
  private wallet_address: string;
  signerType: string = "AWSKMS_SIGNER";
  inner: string = "AWSKMS";

  constructor(_key_id: string, _sub: string, _wallet_address: string) {
    this.key_id = _key_id;
    this.sub = _sub;
    this.wallet_address = _wallet_address;
  }

  async signMessage( message: SignableMessage ): Promise<Hex> {
    const eip191hash = viem.hashMessage(message);

    const signerPayload = {
      operation: 'sign_userop',
      userop_hash: eip191hash,
      key_id: this.key_id,
      sub: this.sub
    };

    const signedPayload = await callSigningFunction(Buffer.from(JSON.stringify(signerPayload)));
    return signedPayload as Hex;
  };
  async signTypedData(): Promise<Hex> {
    throw new Error('Not implemented');
  };
  async getAddress(): Promise<Address> {
    return this.wallet_address as Address;
  }
}

And here is the entire request body:

{
    "method": "eth_sendUserOperation",
    "params": [
        {
            "initCode": "0x000000e92D78D90000007F0082006FDA09BD5f1173876732000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000001000000000000000000000000391ad40d98ab261d6e293ba635dd5bd732ec131c",
            "sender": "0xBAd03Abc633589B616c13A71ff6bEb84B7C92E21",
            "nonce": "0x0",
            "callData": "0xb61d27f6000000000000000000000000ac020e2a1aec9f89d3fba5e8d3b7bd84c1bdc971000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000044b1884744000000000000000000000000000000000000000000000000000000000000012c000000000000000000000000391ad40d98ab261d6e293ba635dd5bd732ec131c00000000000000000000000000000000000000000000000000000000",
            "signature": "c7fec94fc8e5bcab800818765bff310dc6e86f8fc28ab63d6673b57ee3c07e3a3f3db935fb67f61fcaf2c8da4e4693551813a7afc0c5cd7b7cc30668764e19591b",
            "paymasterAndData": "0xc03aac639bb21233e0139381970328db8bceeb670000000000000000668d6cbe00000000000000000000000000000000000000001629cc2c9e824ef81d5aee1a486385100513808f51ad1073742eebda42ece8c468b7b9bd97e2da826e895db91d9b248830bfcb45fef1ab24727f6bf8e55bef361c",
            "maxFeePerGas": "0xa5163da0",
            "maxPriorityFeePerGas": "0x4190ab00",
            "callGasLimit": "0x6bb8",
            "verificationGasLimit": "0xd8274",
            "preVerificationGas": "0xc150"
        },
        "0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789"
    ]
}

[ebaizel]

Of course, I resolved it right after opening this issue 😄

I needed to format the signature in Hex, so adding this line fixed it:

return `0x${signedPayload}` as Hex;