Along with exiting calendar integration, need to integrate with Jira calendar as well.
Could'nt find required API's at this point. Will have to try it again in future to integrate with it based on popularity.
As of now still Jira calendar does not support fetching data using API. So this feature is blocked for implementation.
This is kind of implemented as part of #279, however, those are internal API's and does not work if OAuth implementation is used. So this is still in blocked state.