Ability to trigger Flow from Dynamics 365 (CRM) with HTTP POST

[tdutch]

We have a scenario in Dynamics 365 (Customer Engagement) where users want to be able to click a custom ribbon button to run a Flow. They are getting an error "AuthorizationFailed" and "You do not have permissions to perform action 'run' on scope '/triggers/manual/paths/invoke/".

The custom ribbon button calls a JavaScript function that is available to the form in a Web Resource. The function uses XMLHttpRequest to POST to the URI for the Flow (e.g., https://prod-51.westus.logic.azure.com:443/workflows/{GUID}/triggers/manual/paths/invoke?api-version...}).

The same Flow URI works fine from PostMan.