Restructure solution layout by module

src/__Libraries/StellaOps.Auth.Security/Dpop/DpopNonceUtilities.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace StellaOps.Auth.Security.Dpop;
+
+internal static class DpopNonceUtilities
+{
+    private static readonly char[] Base64Padding = { '=' };
+
+    internal static string GenerateNonce()
+    {
+        Span<byte> buffer = stackalloc byte[32];
+        RandomNumberGenerator.Fill(buffer);
+
+        return Convert.ToBase64String(buffer)
+            .TrimEnd(Base64Padding)
+            .Replace('+', '-')
+            .Replace('/', '_');
+    }
+
+    internal static byte[] ComputeNonceHash(string nonce)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(nonce);
+        var bytes = Encoding.UTF8.GetBytes(nonce);
+        return SHA256.HashData(bytes);
+    }
+
+    internal static string EncodeHash(ReadOnlySpan<byte> hash)
+        => Convert.ToHexString(hash);
+
+    internal static string ComputeStorageKey(string audience, string clientId, string keyThumbprint)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(audience);
+        ArgumentException.ThrowIfNullOrWhiteSpace(clientId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(keyThumbprint);
+
+        return string.Create(
+            "dpop-nonce:".Length + audience.Length + clientId.Length + keyThumbprint.Length + 2,
+            (audience.Trim(), clientId.Trim(), keyThumbprint.Trim()),
+            static (span, parts) =>
+            {
+                var index = 0;
+                const string Prefix = "dpop-nonce:";
+                Prefix.CopyTo(span);
+                index += Prefix.Length;
+
+                index = Append(span, index, parts.Item1);
+                span[index++] = ':';
+                index = Append(span, index, parts.Item2);
+                span[index++] = ':';
+                _ = Append(span, index, parts.Item3);
+            });
+
+        static int Append(Span<char> span, int index, string value)
+        {
+            if (value.Length == 0)
+            {
+                throw new ArgumentException("Value must not be empty after trimming.");
+            }
+
+            value.AsSpan().CopyTo(span[index..]);
+            return index + value.Length;
+        }
+    }
+}