> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dfns.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Development

> Architecture and usage patterns for the Dfns Flutter SDK, including how to authenticate users, sign requests, and integrate with the Dfns API.

## Concepts

### `PasskeysSigner`

All state-changing requests made to the Dfns API need to be cryptographically signed by credentials
registered with the User.

> **Note:** To be more precise, it's not the request itself that needs to be signed, but rather a "
> User Action Challenge" issued by Dfns. For simplicity, we refer to this process as "request
> signing".

This request signature serves as cryptographic proof that only authorized entities are making the
request. Without it, the request would result in an Unauthorized error.
While implementing a Flutter application your backend server will have to communicate with the DFNS API
to retrieve this challenge and pass it to your application, `PasskeysSigner` will be used to
register and authenticate a user.

#### Register

```
final fido2Attestation = await PasskeysSigner.register(challenge);
```

#### Sign

```
final fido2Assertion = await PasskeysSigner.sign(initRes.challenge);
```