Security - Add a appropriate SSL-Cert
every webpage, that is providing a login, should be protected with a working SSL-Cert! Otherwise everyone in the same wifi/network can steal logins or session cookies! There are several other scenarios that apply here!
The current Cert ist twice invalid:
The certificate is not trusted because it is self-signed. The certificate expired on 13.07.2016 21:31. The current time is 09.03.2017 22:42.
For example: Let's encrypt offers free certificates.
If you installed a valid cert, make sure to set the secure flag at the session-cookie :)