Eliminate two hash allocations

Author: iamcarbon

Src/Fido2/AttestationFormat/AndroidSafetyNet.cs

@@ -152,10 +152,11 @@ public override (AttestationType, X509Certificate2[]) Verify()
             {
                 throw new Fido2VerificationException("Nonce value not base64string in SafetyNet attestation", ex);
             }
-            
-            var dataHash = SHA256.HashData(Data);
 
-            if (!dataHash.AsSpan().SequenceEqual(nonceHash))
+            Span<byte> dataHash = stackalloc byte[32];
+            SHA256.HashData(Data, dataHash);
+
+            if (!dataHash.SequenceEqual(nonceHash))
             {
                 throw new Fido2VerificationException($"SafetyNet response nonce / hash value mismatch, nonce {Convert.ToHexString(nonceHash)}, hash {Convert.ToHexString(dataHash)}");
             }

Src/Fido2/AttestationFormat/Apple.cs

@@ -63,7 +63,8 @@ X5c.Values is null || X5c.Values.Count is 0 ||
             var nonceToHash = Data;
 
             // 4. Perform SHA-256 hash of nonceToHash to produce nonce.
-            byte[] nonce = SHA256.HashData(nonceToHash);
+            Span<byte> nonce = stackalloc byte[32];
+            SHA256.HashData(nonceToHash, nonce);
 
             // 5. Verify nonce matches the value of the extension with OID ( 1.2.840.113635.100.8.2 ) in credCert.
             var appleExtensionBytes = GetAppleAttestationExtensionValue(credCert.Extensions);