How-to: Add another wallet owner

Register an additional WebAuthn passkey as an owner on your modular smart contract account (MSCA). Additional owners serve as recovery keys. They extend recovery coverage across additional devices without changing how routine signing works. See How Digital Asset-Backed Borrowing works for the wallet architecture.

Prerequisites

Before you begin, ensure that you’ve:

Completed the Borrow USDC against cirBTC collateral quickstart and provisioned a wallet.
Registered a new WebAuthn passkey on the device you want to add as an owner. Capture the P-256 public key and the WebAuthn credential identifier as hex strings.

Steps

Submit the add-owner request

Call POST /v1/borrow/wallets/owners with the new passkey’s public key and credential ID.

curl -X POST https://api-sandbox.circle.com/v1/borrow/wallets/owners \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "idempotencyKey": "f7a8b9c0-d123-4e56-7890-abcdef123456",
    "ownerKey": "0x04c1d2e3f4051627384950a1b2c3d4e5f60718293a4b5c6d7e8f90a1b2c3d4e5f6",
    "credentialId": "b2c3d4e5f6071829"
  }'

The endpoint returns an onchainJob with jobType: add_owner:

{
  "data": {
    "id": "a7b8c9d0-e123-4567-890a-bcdef1234567",
    "jobType": "add_owner",
    "status": "received",
    "createDate": "2026-06-25T11:00:00.000Z",
    "updateDate": "2026-06-25T11:00:00.000Z"
  }
}

Save the job id. You poll it in the next step.

Wait for the operation to complete

Poll GET /v1/borrow/jobs/{id} until status reaches completed.

{
  "data": {
    "id": "a7b8c9d0-e123-4567-890a-bcdef1234567",
    "jobType": "add_owner",
    "status": "completed",
    "txHash": "0x4d5e6f70819293a4b5c6d7e8f90a1b2c3d4e5f60718293a4b5c6d7e8f9aabbccdd",
    "createDate": "2026-06-25T11:00:00.000Z",
    "updateDate": "2026-06-25T11:01:30.000Z"
  }
}

Confirm the new owner

Fetch the wallet and confirm the new owner appears in the owners array with status: active:

curl https://api-sandbox.circle.com/v1/borrow/wallets \
  -H "Authorization: Bearer $API_KEY"

{
  "data": [
    {
      "id": "9c1b2a3d-4e5f-6071-8293-a4b5c6d7e8f9",
      "walletAddress": "0x742d35Cc6634C0532925a3b844Bc9e7595f9f68C",
      "owners": [
        {
          "id": "1f2e3d4c-5b6a-7980-1234-56789abcdef0",
          "ownerType": "passkey",
          "publicKey": "0x04b0a1c2d3e4f5061728394a5b6c7d8e9f00112233445566778899aabbccddeeff",
          "credentialId": "a1b2c3d4e5f60718",
          "status": "active",
          "addedDate": "2026-06-20T14:10:00.000Z"
        },
        {
          "id": "2e3d4c5b-6a79-8012-3456-789abcdef012",
          "ownerType": "passkey",
          "publicKey": "0x04c1d2e3f4051627384950a1b2c3d4e5f60718293a4b5c6d7e8f90a1b2c3d4e5f6",
          "credentialId": "b2c3d4e5f6071829",
          "status": "active",
          "addedDate": "2026-06-25T11:01:30.000Z"
        }
      ]
    }
  ]
}

The wallet now has two passkey recovery owners. Circle’s ECDSA co-signer continues to sign every UserOperation for the wallet. The additional passkey does not change routine signing behavior.

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How-to: Add another wallet owner

Prerequisites

Steps

​Prerequisites

​Steps

Prerequisites

Steps