I am developing an outlook web addin, in the taskpane I have a cookie sent from the server with httpOnly. For the same session cookie is handled correctly, when I close the task pane and re-open the cookie seems to be cleared. This does not happen on Mac, does not happen on Windows when the browser used by outlook is IE11. Seems to be happening only when the outlook uses edge as it's engine. Is there something I can add in the manifest perhaps to avoid this cookie clearing?
Adding to @BrianClink's response, the session cookie probably works on most versions that use Internet Explorer to load the add-ins. Whenever an add-in is closed, Internet Explorer stays alive for a while, which probably preserves the session cookies. Since we switched to Microsoft Edge, this is no longer the case. So please don't rely on this behavior for preserving cookies.