Hmm, so security plugin is enabled (since you see login page), but your kibana.yml doesn't include username and password for internal Kibana user:
#elasticsearch.username: "user"
#elasticsearch.password: "pass"
Can you please set these and make sure they are correct? If that's the reason you should see something like this in Kibana logs: security_exception\",\"reason\":\"failed to authenticate user ....
Best,
Oleg