Add 5 variable Concat overload

Author: iamcarbon

Src/Fido2/AttestationFormat/FidoU2f.cs

@@ -65,13 +65,13 @@ X5c.Values.Count is 0 ||
             var publicKeyU2F = DataHelper.Concat(stackalloc byte[1] { 0x4 }, x, y);
 
             // 5. Let verificationData be the concatenation of (0x00 || rpIdHash || clientDataHash || credentialId || publicKeyU2F)
-            var verificationData = new byte[1] { 0x00 };
-            verificationData = verificationData
-                                .Concat(AuthData.RpIdHash)
-                                .Concat(clientDataHash)
-                                .Concat(AuthData.AttestedCredentialData.CredentialID)
-                                .Concat(publicKeyU2F.ToArray())
-                                .ToArray();
+            byte[] verificationData = DataHelper.Concat(
+                stackalloc byte[1] { 0x00 },
+                AuthData.RpIdHash,
+                clientDataHash,
+                AuthData.AttestedCredentialData.CredentialID,
+                publicKeyU2F
+            );
 
             // 6. Verify the sig using verificationData and certificate public key
             if (Sig is null || Sig.Type != CBORType.ByteString || Sig.GetByteString().Length is 0)

Src/Fido2/Extensions/DataHelper.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 
 namespace Fido2NetLib
 {
@@ -24,5 +25,27 @@ public static byte[] Concat(ReadOnlySpan<byte> a, ReadOnlySpan<byte> b, ReadOnly
 
             return result;
         }
+
+        public static byte[] Concat(ReadOnlySpan<byte> a, ReadOnlySpan<byte> b, ReadOnlySpan<byte> c, ReadOnlySpan<byte> d, ReadOnlySpan<byte> e)
+        {
+            var result = new byte[a.Length + b.Length + c.Length + d.Length + e.Length];
+
+            var position = 0;
+            a.CopyTo(result);
+            position += a.Length;
+            
+            b.CopyTo(result.AsSpan(position));
+            position += b.Length;
+
+            c.CopyTo(result.AsSpan(position));
+            position += c.Length;
+
+            d.CopyTo(result.AsSpan(position));
+            position += d.Length;
+
+            e.CopyTo(result.AsSpan(position));
+
+            return result;
+        }
     }
 }