The API Co-Signer is a component that holds an MPC key share of your Fireblocks Vault and a Configuration Change Key for automated signing and approvals. The key share is used to securely sign transactions initiated via the API. The Configuration Change Key is used to approve new unmanaged wallet additions in the Vault.
You can provision the API Co-Signer with a Co-Signer Callback Handler. The Callback Handler is a predefined HTTPS server that receives signing requests from the API Co-Signer and returns either an approval or rejection response.
- Learn more about installing and maintaining the API Co-Signer in our Help Center.
- Learn more about the Callback Handler structure.