[Security] Add challenge-response auth with scrypt verifiers and stop storing plaintext passwords

Challenge-response authentication: the client derives a scrypt verifier
(RFC 7914, EVP_PBE_scrypt, N=32768, r=8, p=1) and authenticates with
HMAC-SHA256(key, nonce), so neither the password nor its hash is
transmitted. The stored format becomes
"$scrypt$<n>$<r>$<p>$<salt>$<verifier>" and Response_PasswordSalt
now carries the cost parameters. Strict servers only accept scrypt
verifiers; legacy accounts are migrated after a successful login.

Fix #344 for challenge-response servers: a saved profile stores the
derived verifier under the password key instead of the plaintext password.
The connect dialog loads it without revealing it, autoconnect passes it
through, the change-password dialog no longer prefills the old password
field with it, and the client only persists the verifier when
"Save password" is checked.

Took 3 minutes

Took 1 minute

Took 10 seconds

Took 7 minutes

libcockatrice_network/libcockatrice/network/server/remote/server.h

@@ -85,6 +85,11 @@ public:
     {
         return QMap<QString, bool>();
     }
+    /** @brief True when only challenge-response logins are accepted (strict mode). */
+    virtual bool requiresChallengeResponseAuth() const
+    {
+        return false;
+    }
     void addClient(Server_ProtocolHandler *player);
     void removeClient(Server_ProtocolHandler *player);
     QList<QString> getOnlineModeratorList() const;

libcockatrice_network/libcockatrice/network/server/remote/server_database_interface.h

@@ -40,6 +40,14 @@ public:
     {
         return {};
     }
+    virtual QString getUserPasswordData(const QString & /* user */)
+    {
+        return {};
+    }
+    virtual bool submitPasswordVerifier(const QString & /* user */, const QString & /* passwordVerifier */)
+    {
+        return false;
+    }
     virtual QMap<QString, ServerInfo_User> getBuddyList(const QString & /* name */)
     {
         return QMap<QString, ServerInfo_User>();

libcockatrice_network/libcockatrice/network/server/remote/server_protocolhandler.cpp

@@ -44,6 +44,22 @@ Server_ProtocolHandler::~Server_ProtocolHandler()
 {
 }
 
+void Server_ProtocolHandler::setAuthNonce(const QByteArray &nonce)
+{
+    authNonce = nonce;
+    authNonceCreated = QDateTime::currentDateTimeUtc();
+}
+
+bool Server_ProtocolHandler::isAuthNonceValid(const QByteArray &nonce) const
+{
+    return !authNonce.isEmpty() && authNonce == nonce && authNonceCreated.secsTo(QDateTime::currentDateTimeUtc()) < 60;
+}
+
+void Server_ProtocolHandler::clearAuthNonce()
+{
+    authNonce.clear();
+}
+
 // This function must only be called from the thread this object lives in.
 // Except when the server is shutting down.
 // The thread must not hold any server locks when calling this (e.g. clientsLock, roomsLock).
@@ -507,6 +523,16 @@ Response::ResponseCode Server_ProtocolHandler::cmdLogin(const Command_Login &cmd
         return Response::RespContextError;
     }
 
+    // In strict mode only challenge-response logins are accepted.
+    if (server->requiresChallengeResponseAuth() &&
+        (!cmd.has_hashed_password() || cmd.hashed_password().rfind("$challenge$", 0) != 0)) {
+        auto *re = new Response_Login;
+        re->set_denied_reason_str("Client upgrade required");
+        re->add_missing_features("challenge_response_auth");
+        rc.setResponseExtension(re);
+        return Response::RespClientUpdateRequired;
+    }
+
     // check client feature set against server feature set
     FeatureSet features;
     QMap<QString, bool> receivedClientFeatures;

libcockatrice_network/libcockatrice/network/server/remote/server_protocolhandler.h

@@ -4,6 +4,8 @@
 #include "server.h"
 #include "server_abstractuserinterface.h"
 
+#include <QByteArray>
+#include <QDateTime>
 #include <QObject>
 #include <libcockatrice/protocol/pb/response.pb.h>
 #include <libcockatrice/protocol/pb/server_message.pb.h>
@@ -55,6 +57,8 @@ protected:
     bool acceptsUserListChanges;
     bool acceptsRoomListChanges;
     bool idleClientWarningSent;
+    QByteArray authNonce;
+    QDateTime authNonceCreated;
     virtual void logDebugMessage(const QString & /* message */)
     {
     }
@@ -124,6 +128,13 @@ public:
         return databaseInterface;
     }
 
+    /** @brief Store a fresh challenge nonce for the next challenge-response login attempt. */
+    void setAuthNonce(const QByteArray &nonce);
+    /** @brief True if nonce matches the pending one and was issued less than 60 seconds ago. */
+    bool isAuthNonceValid(const QByteArray &nonce) const;
+    /** @brief Invalidate the pending nonce (single-use). */
+    void clearAuthNonce();
+
     int getLastCommandTime() const
     {
         return timeRunning - lastDataReceived;