jwt-express.js
function() {
        return {
            token: this.token,
            payload: this.payload,
            valid: this.valid,
            expired: this.expired,
            stale: this.stale
        };
    }
function() {
        return {
            token: this.token,
            payload: this.payload,
            valid: this.valid,
            expired: this.expired,
            stale: this.stale
        };
    }
toJSON - this function is called when the jwt is passed through JSON.stringify
we don't want the secret or options to be stringified
@return object