feat(fido2): WebAuthn previewSign extension (ARKG-P256)

Yubico.Core/src/Yubico/Core/Cryptography/ArkgPrimitives.cs

@@ -0,0 +1,47 @@
+// Copyright 2025 Yubico AB
+//
+// Licensed under the Apache License, Version 2.0 (the "License").
+// You may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace Yubico.Core.Cryptography
+{
+    /// <summary>
+    /// Factory for the default <see cref="IArkgPrimitives"/> implementation.
+    /// </summary>
+    /// <remarks>
+    /// This factory creates instances of the platform-specific ARKG-P256
+    /// cryptographic primitives implementation. The default implementation
+    /// uses OpenSSL via P/Invoke through the Yubico.NativeShims library.
+    /// </remarks>
+    public static class ArkgPrimitives
+    {
+        /// <summary>
+        /// Creates the OpenSSL-backed ARKG primitives instance.
+        /// </summary>
+        /// <returns>
+        /// An <see cref="IArkgPrimitives"/> implementation that performs
+        /// ARKG-P256 operations using OpenSSL.
+        /// </returns>
+        /// <remarks>
+        /// <para>
+        /// This method returns a new instance on each call. The implementation
+        /// is stateless and thread-safe.
+        /// </para>
+        /// <para>
+        /// For testing or custom implementations, applications can replace the
+        /// default factory by setting the <c>ArkgPrimitivesCreator</c> property
+        /// in <c>Yubico.YubiKey.Cryptography.CryptographyProviders</c>.
+        /// </para>
+        /// </remarks>
+        public static IArkgPrimitives Create() => new ArkgPrimitivesOpenSsl();
+    }
+}