How to Detect if Office 365 web addin is installed or not?

Question

We have a desktop app with which we want to integrate Office 365 calendar. We will have our users provide their consent by authorising the app in office 365. I wonder if I can use any specific permission and/or api that would help us know if our office 365 office.js addin is installed by that user. This works great with VSTO addin as we can get the info from system registry, however, as Office 365 addin is installed on cloud no such registry can be found and we won’t be able to know.

Answer 1

Exchange will create a subfolder for each installed web addin in a special folder named WebExtAddins. The folder is on the same level as the other special folders (e.g. the Inbox), but is hidden. You can see that folder (and its subfolders) in OutlookSpy (I am its author) - click IMsgStore button on the OutlookSpy ribbon, click "Open Folder", double click on the folder named WebExtAddins.

UPDATE April 2022 - it looks like Outlook no longer uses the WebExtAddins folder. Instead, the list of web addins is stored in a hidden (associated) message with the message class of "IPM.Configuration.ExtensionMasterTable" in the Inbox folder. The list is stored in the PR_ROAMING_XMLSTREAM binary property. The format of the property is not documented.

In EWS, the list of installed addins can be retrieved using the GetAppManifests operation. If you are using Outlook Object Model or Extended MAPI, your only option is parsing that blob.

For this particular case (figure out if a web addin is installed), the addin custom storage will be in a hidden (associated) message in Inbox folder with the message class of "IPM.Configuration.ClientExtension.<guid>", where <guid> is your addin's GUID. You should be able to asccess that hidden message using MAPIFolder.GetStorage("IPM.Configuration.ClientExtension.<guid>", olIdentifyByMessageClass) (where MAPIFolder is retrieved from Namespace.GetDefaultFolder(olFolderInbox))

Answer 2

It seems that there is no good way to check directly now. Just like you said?Office 365 add-in is installed on Cloud. Since it runs through a separate browser process (Like IE). After plug-ins are loaded, we typically see two IE processes in the process manager. Here's a detail. If your Office is 32-bit, then its core process will be a 32-bit one. You can see that if you load multiple plug-ins, the memory it uses will gradually increase. However, it is still a process.

Screenshot?

Also, if your Windows is 64-bit, it will create another 64-bit IE process which is actually a call relationship. As you can see from the diagram below, the 32-bit process is actually calling the 64-bit process.