One of the top feature requests since the release of Microsoft Planner has been the ability to synchronize Planner tasks with Outlook. After a few years, Microsoft has delivered this capability. Sort of.
The obvious place to synchronize a Planner task would be into the Outlook tasks. But in Q1 of this year, Microsoft announced that Planner tasks can be added to the Outlook calendar as an iCalendar feed. The feature is enabled by default as it gets rolled out to Office 365 tenants.
You can also integrate Planner tasks and Outlook tasks using Flow, but I don't count that as proper integration. Microsoft controls all the plumbing on the back end to make Outlook and Planner integration work, and I don't think it should rely on users creating their own Flows that provide a limited experience anyway.
The iCalendar feed offers a limited view of Planner tasks based on their due date. Little detail is included with the calendar item, but you can click through to Planner to interact with the task.
Users can publish their tasks from within the My Tasks view of Planner.
Something that may raise concerns for some organizations is that the iCalendar feed is accessible by anyone who happens to know the URL. If you have multi-factor authentication requirements, or any other security measures in place such as conditional access or risk-based sign-in policies, none of that appears to make any difference to whether the URL is accessible by someone outside of your organization.
The risk in this situation is probably quite low. The iCalendar link is an obscure URL that would be difficult to guess. And the information included in the iCalendar feed is minimal. For example, descriptions, sub-tasks, and comments on a Planner task, any of which might contain sensitive information, are not included in the iCalendar feed. But for some customers any level of exposure is not acceptable, so it's up to you how you interpret the risk here.
Fortunately, you can turn off the iCalendar publishing option. Microsoft has provided a support article with the steps that you can follow to check your configuration, or disable/enable Outlook calendar sync.
The process is a bit awkward, and the documentation appears to have an error. Where Microsoft advises to name the PowerShell module and manifest files as SetPlannerTenantSettings.psm1 and SetPlannerTenantSettings.psd1 respectively, I recommend you instead use SetTenantSettings.psm1 and SetTenantSettings.psd1. I had errors trying to follow the support guidance until I renamed the files. You might also need to unblock the downloaded DLL files before they will work for you, but my testing wasn't conclusive either way on that point.
Once you have that all set up, you can use the Set-PlannerConfiguration and Get-PlannerConfiguration functions to manage the setting.
PS C:\Scripts\PlannerTenantSettings\lib\net45> Get-PlannerConfiguration
PS C:\Scripts\PlannerTenantSettings\lib\net45> Set-PlannerConfiguration -AllowCalendarSharing $false
Annoyingly, you will need to authenticate each time you run one of the functions.
Calendar sharing is the only Planner setting that is manageable with those functions. Perhaps there will be a fully functional, and easier to use, PowerShell module released some time in the future. For now, this is better than nothing.
Hopefully in the near future we'll see full Planner tasks integration with Outlook tasks. It's not currently on the roadmap, but the customer demand is definitely there.