Core/Authserver: Authserver cleanup (PR#25093)

- Fix a handful of 1/256 bugs with most significant byte zero in BigNumber
- Get rid of (most of) the C-style arrays in authserver
- CryptoRandom as a unified source for cryptographic randomness
- Bring our other crypto APIs into 2020
- BigNumber usability improvements
- Authserver is now actually readable as a result of all of the above

(cherry picked from commit 210176fd91)

src/common/Cryptography/CryptoRandom.cpp

@@ -0,0 +1,26 @@
+/*
+ * This file is part of the TrinityCore Project. See AUTHORS file for Copyright information
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "CryptoRandom.h"
+#include "Errors.h"
+#include <openssl/rand.h>
+
+void Trinity::Crypto::GetRandomBytes(uint8* buf, size_t len)
+{
+    int result = RAND_bytes(buf, len);
+    ASSERT(result == 1, "Not enough randomness in OpenSSL's entropy pool. What in the world are you running on?");
+}