HTTPS/CORS improvements: Enable CORS for player connections, secure session cookies, add certificate endpoint, nginx CORS headers

app/extensions.py

@@ -7,6 +7,7 @@ from flask_bcrypt import Bcrypt
 from flask_login import LoginManager
 from flask_migrate import Migrate
 from flask_caching import Cache
+from flask_cors import CORS
 
 # Initialize extensions (will be bound to app in create_app)
 db = SQLAlchemy()
@@ -14,6 +15,7 @@ bcrypt = Bcrypt()
 login_manager = LoginManager()
 migrate = Migrate()
 cache = Cache()
+cors = CORS()
 
 # Configure login manager
 login_manager.login_view = 'auth.login'