> ## 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.

# Overview

> Shared concepts for client-side Dfns SDKs

Frontend SDKs run on the user's device — browser, mobile app, or hybrid framework. They handle passkey-based signing so users can authorize actions using biometrics or security keys, without your backend ever touching their private credentials.

<Warning>
  Frontend SDKs are designed for [delegated signing](/sdks/backend#delegated-signing). They do not make API calls directly — they sign challenges that your backend initiates. You need a [backend SDK](/sdks/backend) (or direct API integration) to complete the flow.
</Warning>

## How it works

Frontend SDKs implement the signing side of the delegated flow:

1. Your **backend** initiates a state-changing operation and receives a challenge from Dfns
2. Your backend sends the challenge to the **frontend**
3. The frontend SDK signs the challenge using the user's passkey (biometrics, security key, etc.)
4. The frontend sends the signed challenge back to your **backend**
5. Your backend completes the operation with the signed challenge

This ensures that private key material never leaves the user's authenticator, and your backend never has access to user credentials.

## Passkeys

All frontend SDKs use [WebAuthn / passkeys](https://webauthn.io/) for signing. This means:

* The user's private key is stored securely in their authenticator (Touch ID, Face ID, YubiKey, etc.)
* Signing is triggered by a biometric prompt — no passwords involved
* The private key never leaves the device

Each SDK provides a `PasskeysSigner` (or equivalent) that handles the register and sign operations:

* **Register**: creates a new credential (passkey) for the user during onboarding
* **Sign**: signs a User Action Challenge when the user authorizes an operation

## Integration with backend

Your backend uses a `DfnsDelegatedApiClient` (or equivalent) to initiate operations and receive challenges. See the [delegated signing guide](/sdks/backend#delegated-signing) for the backend side, and [implementing delegated wallets](/guides/developers/delegated-wallets) for a full end-to-end tutorial.