Document Kubernetes Kit backend session expiration policy

[TatuLund]

See: https://github.com/vaadin/kubernetes-kit/pull/163/files

[mcollovati]

By implementing the SessionExpirationPolicy interface, the developer can define the expiration timeout.
However, the property does not define the timeout value, but the amount of time to be added to the HTTP session timeout to determine the expiration of the backend session. If time unit is not given, milliseconds is assumed.

[mcollovati]

It would be nice to add also a SessionExpirationPolicy implementation example

[TatuLund]

Thanks for clarification

[TatuLund]

Should this suffice for code example?

    @Bean
    SessionExpirationPolicy sessionExpirationPolicy() {
        return Duration.ofMinutes(60);
    }

[mcollovati]

The SessionExpirationPolicy.apply() method takes current HTTP session timeout as argument

@Bean
SessionExpirationPolicy sessionExpirationPolicy() {
    return sessionTimeout -> Duration.ofMinutes(60);
}

[MatthewVaadin]

If time unit is not given, milliseconds is assumed.

This may be the default, but it's not particularly useful. If seconds are more appropriate, perhaps the property should be annotated with @DurationUnit(ChronoUnit.SECONDS) and the original phrasing kept?

[mcollovati]

Sound a good idea