Auth Cookie Support (#285)

* Auth cookie support

* Add config option for auth cookie support

* Safe handling of TEGid/auth_id strings

* Fix bad size calculation due to pointer cast

* Expiration timestamp instead of valid bit

* Change setting to "allowed auth methods"

This allows plaintext password auth to be disabled altogether

* PR feedback

src/settings.hpp

@@ -8,6 +8,7 @@ namespace settings {
     extern int LOGINPORT;
     extern bool APPROVEALLNAMES;
     extern bool AUTOCREATEACCOUNTS;
+    extern std::string AUTHMETHODS;
     extern int DBSAVEINTERVAL;
     extern int SHARDPORT;
     extern std::string SHARDSERVERIP;