OrientDB Security - Javascript
You should use some backend technology/framework to abstract direct access to OrientDB so that users can't manipulate your database directly. You can try to look at node.js for example if you like to work with JavaScript.
You can ask to the client to enter username/password and just let a "guest" user to see the public pages.
I would recommend not having the front-end communicate directly with the database as this would make it harder to secure and harder to protect against injections.
Using some back-end code would be better suited to communicating with the database.