> For the complete documentation index, see [llms.txt](https://docs.wisej.com/extensions/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.wisej.com/extensions/extensions/webauthn.md).

# WebAuthn

Wisej.NET's WebAuthn extension is an integration for the [Web Authentication API](https://webauthn.guide/) available in most browsers.

{% embed url="<https://github.com/iceteagroup/wisej-extensions/tree/main/Wisej.Ext.WebAuthn>" %}
WebAuthn Source Code
{% endembed %}

## Features

* WebAuthn API wrapper with async client calls for credential creation and assertion retrieval&#x20;
* Server-side signature validation for ES256 and RS256, plus signature parsing utilities
* Data models for authenticator/client data and responses&#x20;
* WebAuthn request/selection structures (relying party, user entity, credential parameters and descriptors, authenticator selection criteria).&#x20;
* Spec enums and flags for attestation, attachments, transports, resident key requirements, and COSE algorithms.

## Code Example

This code sample sets up all the parameters to call the WebAuthn.CreateAsync function. The WebAuthn.CreateAsync function asks the browser’s WebAuthn API to create a new credential using a local authenticator (e.g., Windows Hello, Touch ID, etc.), honoring the authenticator selection settings and timeout.  It then returns a response object that includes the new credential’s public key, authenticator data, and client data.

```csharp
    // Create a random challenge (base64 string is typical)
    // Use a 33-byte challenge to avoid Base64 padding (length divisible by 3).
    var challengeBytes = new byte[33];
    using (var rng = RandomNumberGenerator.Create())
    {
        rng.GetBytes(challengeBytes);
    }
    var challenge = Convert.ToBase64String(challengeBytes);

    var rp = new RelyingParty("example.com", "Example App");

    // Use a 12-byte user id to avoid Base64 padding.
    var userIdBytes = Encoding.UTF8.GetBytes("user-123-abc");
    var user = new PublicKeyCredentialUserEntity(
            id: Convert.ToBase64String(userIdBytes),
            name: "user@example.com",
            displayName: "User");

    var publicKeyCredentialParameters = new[]
    {
        new PublicKeyCredentialParameters(COSEAlgorithmIdentifier.ES256),
        new PublicKeyCredentialParameters(COSEAlgorithmIdentifier.RS256),
};

    var authenticatorSelection = new AuthenticatorSelectionCriteria(
            AuthenticatorAttachment.Platform,
            residentKey: "",
            requireResidentKey: false,
            userVerification: ResidentKeyRequirement.Preferred);

    var timeout = 60000;

    var response = await WebAuthn.CreateAsync(
            challenge,
            rp,
            user,
            publicKeyCredentialParameters,
            authenticatorSelection,
            timeout,
            AttestationConveyancePreference.None);
            
    // Persist response.AuthenticatorData.PublicKey and
    // verify response.ClientData.Challenge on the server.
```

## How to use

The WebAuthn extension can be added to a Wisej.NET project using NuGetPackage Manager.

{% embed url="<https://www.nuget.org/packages/Wisej-3-WebAuthn>" %}