What is the _doc property on the object received in the findOne callback in Mongoose?

Question

MongoDB

What's the difference between the document object itself and the object obtained from that object's _doc property? In the logs, it displays the same thing, except that the order of the properties in the object changes. However, in the code I'm parsing, it is the _doc variant that is used to create the json web token.

User.findOne({username: request.body.username}, (error, document) => {
console.log(document._doc)
console.log(document);
token = jwt.sign(document._doc, config.secret);