Oauth Authentication for SharePoint REST API

Question

Based on my research and this Video, I was under the impression that switching between the Graph API and the SharePoint REST API should be pretty straight forward.

• After obtaining an OAuth2 token, I am able to access the Graph API with a call such as: https://graph.microsoft.com/v1.0/sites/root/drives.

• However calling the SharePoint Api as documented:
  http://<my_tenant>/site/_api/lists fails with:

  {"error_description":"Invalid issuer or signature."}
  

Is a different token required for the REST API? How can I acquire it?

Answer 1

As of this moment, access to SharePoint endpoint via Graph API is possible only through the beta endpoint.

Your URL should be as below:

https://graph.microsoft.com/beta/sites/tenantname.sharepoint.com/lists

Make a normal GET call to the above endpoint, the output would be as below:

Reference - Working with SharePoint sites in Microsoft Graph

To access the http://<my_tenant>/site/_api/lists endpoint, Graph API token wont work.

If you are logged into SharePoint you don't need any token at all to make a get request (pure client-side solution). When you make the below call, it gets the data based on your permissions.

$.ajax({
           url: "https://sitecollectionurl/_api/web/lists",
           method: "GET",
           headers: { "Accept": "application/json; odata=verbose" },
           success: function (data) {
                console.log(data);
          },
          error: function (data) {
              console.log("sowmthing went wrong: "+ data);
         }
});

Also, you can use the excellent Graph explorer to test your Graph API calls. Here, select the version as beta and you can see the data from your sharepoint lists.

Graph Explorer

Answer 2

If there is a 401-Error on request (test in browser) the error includes detailed information about the authentication you need.