public static ReadOnlyMemory <byte> GetOctetStringBytes(this AsnReader reader, Asn1Tag expectedTag)
        {
            if (reader.TryGetPrimitiveOctetStringBytes(expectedTag, out ReadOnlyMemory <byte> contents))
            {
                return(contents);
            }

            // Guaranteed too big, because it has the tag and length.
            int length = reader.PeekEncodedValue().Length;

            byte[] rented = ArrayPool <byte> .Shared.Rent(length);

            try
            {
                if (reader.TryCopyOctetStringBytes(expectedTag, rented, out int bytesWritten))
                {
                    return(new ReadOnlyMemory <byte>(rented.AsSpan(0, bytesWritten).ToArray()));
                }

                Debug.Fail("TryCopyOctetStringBytes produced more data than the encoded size");
                throw new CryptographicException();
            }
            finally
            {
                Array.Clear(rented, 0, length);
                ArrayPool <byte> .Shared.Return(rented);
            }
        }