Natas 5

After logging in we see

Access disallowed, you are not logged in, so first things first I decided to inspect the webpage.

Under the Application tab we see loggedin has a value of 0, lets try changing that to 1

And after reloading we can see that the flag is shown

Access granted. The password for natas6 is 0RoJwHdSKWFTYR5WuiAewauSuNaBXned