如何使用 EWS 令牌通过后端 API 从 Microsoft Graph API 获取附件？

Question

I have an EWS token and attachment details as payload sent from an Outlook add-in. I am trying to use the Microsoft Graph API to fetch the content of the attachment in base64 format and save it in an AWS S3 Bucket.

My plan is to use the following API endpoint:

https://graph.microsoft.com/v1.0/me/messages/${itemId}/attachments` (/${attachmentId})

However, when I try to use the EWS token as the access token for this request, I get an "Access token validation failure. Invalid audience." error. How can I obtain a valid access token for this request and successfully fetch the attachments?

I tried using npm packages like node-ews and ews-javascript-api.

I tried using the above endpoint and token-exchange grant type too. 

Alternate (better) methods are also welcomed.

Answer 1

EWS and Graph API are different technologies. You can't use EWS token for accessing Graph API. To access data through Microsoft Graph, your application will need to acquire an OAuth 2.0 access token, and present it to Microsoft Graph in either of the following options:

1. The HTTP Authorization request header, as a Bearer token
2. The graph client constructor, when using a Microsoft Graph client library Use the Microsoft Authentication Library API, MSAL to acquire the access token to Microsoft Graph.

Read more about that in the Best practices for working with Microsoft Graph article.