feat: sign in with a passkey (WebAuthn, ES256, discoverable credentials) and manage your passkeys [CI]

backend/src/MoShiro.Backend.Application/Auth/WebAuthnRegistration.cs

@@ -0,0 +1,177 @@
+using System.Security.Cryptography;
+using System.Text;
+using Fleet.Identity;
+
+namespace MoShiro.Backend.Application;
+
+/// <summary>注册成功后要保存的凭证。</summary>
+public sealed record RegisteredCredential(byte[] CredentialId, byte[] PublicKeySpki, uint SignCount);
+
+/// <summary>
+/// 解析并校验 WebAuthn 注册（<c>navigator.credentials.create</c> 的结果）。只接受 ES256；attestation 一律当 <c>none</c> 处理：
+/// 不验设备证明，信任浏览器的实现（docs/access.md）。CBOR 解析只在 Backend 里，节点不带。
+/// </summary>
+public static class WebAuthnRegistration
+{
+    public static RegisteredCredential? Verify(
+        ReadOnlySpan<byte> attestationObject, ReadOnlySpan<byte> clientDataJson, string rpId, ReadOnlySpan<byte> expectedChallenge,
+        Func<string, bool> originAllowed, bool requireUserVerification)
+    {
+        if (!WebAuthnAssertion.ClientDataValid(clientDataJson, "webauthn.create", expectedChallenge, originAllowed))
+        {
+            return null;
+        }
+
+        try
+        {
+            if (new MiniCbor(attestationObject.ToArray()).ReadValue() is not Dictionary<object, object> attestation
+                || attestation.GetValueOrDefault("authData") is not byte[] authData || authData.Length < 55)
+            {
+                return null;
+            }
+
+            if (!CryptographicOperations.FixedTimeEquals(authData.AsSpan(0, 32), SHA256.HashData(Encoding.UTF8.GetBytes(rpId))))
+            {
+                return null;
+            }
+
+            byte flags = authData[32];
+            const byte attestedData = 0x40;
+            if ((flags & WebAuthnAssertion.FlagUserPresent) == 0 || (flags & attestedData) == 0 || (requireUserVerification && (flags & WebAuthnAssertion.FlagUserVerified) == 0))
+            {
+                return null;
+            }
+
+            uint signCount = (uint)((authData[33] << 24) | (authData[34] << 16) | (authData[35] << 8) | authData[36]);
+            int idLength = (authData[53] << 8) | authData[54];
+            if (idLength is 0 or > 1023 || authData.Length < 55 + idLength)
+            {
+                return null;
+            }
+
+            byte[] credentialId = authData[55..(55 + idLength)];
+            var reader = new MiniCbor(authData[(55 + idLength)..]);
+            if (reader.ReadValue() is not Dictionary<object, object> cose
+                || cose.GetValueOrDefault(1L) is not long kty || kty != 2
+                || cose.GetValueOrDefault(3L) is not long alg || alg != -7
+                || cose.GetValueOrDefault(-1L) is not long curve || curve != 1
+                || cose.GetValueOrDefault(-2L) is not byte[] { Length: 32 } x
+                || cose.GetValueOrDefault(-3L) is not byte[] { Length: 32 } y)
+            {
+                return null;
+            }
+
+            using ECDsa key = ECDsa.Create(new ECParameters { Curve = ECCurve.NamedCurves.nistP256, Q = new ECPoint { X = x, Y = y } });
+            return new RegisteredCredential(credentialId, key.ExportSubjectPublicKeyInfo(), signCount);
+        }
+        catch (Exception ex) when (ex is InvalidDataException or CryptographicException or ArgumentException or IndexOutOfRangeException)
+        {
+            return null;
+        }
+    }
+}
+
+/// <summary>够用的 CBOR 读取器（RFC 8949）：整数、字节串、文本串、数组、映射、布尔和 null。输入有上限，嵌套有深度限制。</summary>
+internal sealed class MiniCbor
+{
+    private const int MaxDepth = 8;
+    private const int MaxItems = 64;
+
+    private readonly byte[] _data;
+    private int _position;
+
+    public MiniCbor(byte[] data)
+    {
+        _data = data;
+    }
+
+    public object? ReadValue(int depth = 0)
+    {
+        if (depth > MaxDepth || _position >= _data.Length)
+        {
+            throw new InvalidDataException("cbor too deep or truncated");
+        }
+
+        byte initial = _data[_position++];
+        int major = initial >> 5;
+        long argument = ReadArgument(initial & 0x1F);
+        switch (major)
+        {
+            case 0:
+                return argument;
+            case 1:
+                return -1 - argument;
+            case 2:
+                return Take(argument);
+            case 3:
+                return Encoding.UTF8.GetString(Take(argument));
+            case 4:
+                {
+                    CheckCount(argument);
+                    var list = new List<object?>();
+                    for (long i = 0; i < argument; i++)
+                    {
+                        list.Add(ReadValue(depth + 1));
+                    }
+
+                    return list;
+                }
+
+            case 5:
+                {
+                    CheckCount(argument);
+                    var map = new Dictionary<object, object>();
+                    for (long i = 0; i < argument; i++)
+                    {
+                        object key = ReadValue(depth + 1) ?? throw new InvalidDataException("null map key");
+                        map[key] = ReadValue(depth + 1)!;
+                    }
+
+                    return map;
+                }
+
+            case 7:
+                return initial switch { 0xF4 => false, 0xF5 => true, 0xF6 => null, _ => throw new InvalidDataException("unsupported simple value") };
+            default:
+                throw new InvalidDataException("unsupported cbor type");
+        }
+    }
+
+    private long ReadArgument(int info)
+    {
+        if (info < 24)
+        {
+            return info;
+        }
+
+        int length = info switch { 24 => 1, 25 => 2, 26 => 4, 27 => 8, _ => throw new InvalidDataException("indefinite lengths are not supported") };
+        byte[] bytes = Take(length);
+        long value = 0;
+        foreach (byte b in bytes)
+        {
+            value = (value << 8) | b;
+        }
+
+        return value < 0 ? throw new InvalidDataException("argument too large") : value;
+    }
+
+    private byte[] Take(long length)
+    {
+        if (length < 0 || length > _data.Length - _position)
+        {
+            throw new InvalidDataException("cbor truncated");
+        }
+
+        byte[] result = _data[_position..(_position + (int)length)];
+        _position += (int)length;
+        return result;
+    }
+
+    private static void CheckCount(long count)
+    {
+        if (count > MaxItems)
+        {
+            throw new InvalidDataException("cbor collection too large");
+        }
+    }
+}