Outlook Add-in: questions about calling EWS

Question

We have an Outlook office.js API add-in that customizes meetings using a task pane the user opens from an add-in command while editing a meeting. We need information from the meeting that is not exposed by the office.js API. We can use the Outlook REST API or the Microsoft Graph API for our Office 365 users, but for those users on Exchange 2013+ On-Premise I believe we need to use EWS (correct?).

This is new to me so if I may, I have some questions:

1. I read that "The server administrator must set OAuthAuthentication to true on The Client Access Server EWS directory to enable the makeEwsRequestAsync method to make EWS requests." This seems like a serious limitation. Is there anyway around this? We want the add-in to be completely user-installable.
2. All the examples I've seen make use of makeEwsRequestAsync. What is ewsUrl used for? Can someone point me to an example?
3. Can someone recommend some good links?

Thanks.

Answer 1

Without OAuthAuthentication enabled, there would be no way authenticate the user. Keep in mind that your add-in is running on your web server. Outlook uses OAUTH to authenticate the user and allow your web app to make an EWS request on that user's behalf.

The most common use of the ewsUrl is to get attachments of an Outlook item from the server.