Is it safe to use Play's JavaSessions to authenticate users?

[teabooger]

At first glance, the article https://www.playframework.com/documentation/3.0.x/JavaSessionFlash allows to easily implement the form-based authentication, setting the necessary time of expiration for session and transferring the token to the server. However, I am embarrassed by the lack of notes about security, like it was in the forms example. Therefore, I had the idea that these sessions are not intended for storage of such sensitive data as auth tokens. As a result, is it suitable and safe tool for authorizing users?