How can my third party application access on-premise users calendar using modern authentication via EWS API?

Question

I have a third party application wherein some of my users are using On-Premise Exchange server,

How can I access or create calendar events in their on-premise Outlook account using modern authentication?

We were able to fetch calendar events by authenticating users via NTLM method & using EWS API, but we don't want to store users password on our server & we are looking for token based system

Can someone help how we can fetch/create/update events for completely on-premise Exchange Server 2019 (CU14) clients, what should we ask our clients to do on their end?

Please let us know if there are any other possibilities as well in doing above with less efforts on both the sides

Thank you

Answer 1

Hi @Aliraza HN

For fetch/create/update events, it is recommended that you use the Graph API, which provides an endpoint for each function, see the link for details:

https://learn.microsoft.com/en-us/graph/api/user-list-events?view=graph-rest-1.0&tabs=http

https://learn.microsoft.com/en-us/graph/api/user-post-events?view=graph-rest-1.0&tabs=http

https://learn.microsoft.com/en-us/graph/api/event-update?view=graph-rest-1.0&tabs=http

Importantly, to access the Graph API, you need to first register your app in Azure and then get an access token.

There are two recommended ways to obtain the access token. One is to use Auth code flow, which requires the user to log in interactively and grant corresponding delegated permissions. For details, see this case.

The other option is to use Client credentials flow. This mode does not require user participation, but requires the administrator to grant corresponding application permissions. For details, see Example.

Hope this helps.

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