You can turn off security entirely, which will disable the login screen, by setting
xpack.security.enabled: false in elasticsearch.yml and kibana.yml, but that may not be what need.
It can be done with a reverse proxy. May be pass a valid Basic Authorization header with the request will validate the session, creating and using an authorization cookie in the background may be by using an nginx proxy.
some more discussions around that: Auto-authenticating to iframe-embedded Kibana dashboard
hope it helps
Rashmi