Office Outlook Add-in- Adding an attachment from a secure location - outlook

Question

I'm adding an "Add attachment" command as part of an Office Outlook add-in.
I want to find a way to add file from a URL with authorization.
I thought downloading it with ajax and then saving it from a blob but looks like the command won't support it.
My code testing it that fails:
const text = 'attachment content';
const blob = new Blob([text], {type: 'text/plain'});
const attachmentURI = window.URL.createObjectURL(blob);
Office.context.mailbox.item.addFileAttachmentAsync(
attachmentURI,
'file.txt',
{ asyncContext: null },
function (asyncResult) {
if(asyncResult.status == Office.AsyncResultStatus.Failed){
console.log('error adding attachment: ' + asyncResult.error.message);
}
else {
const attachmentID = asyncResult.value;
console.log('added attachment: ' + attachmentID);
}
}
);
Any suggestions on saving an attachment from a URL with permissions?
Function documentation:
https://dev.office.com/docs/add-ins/outlook/add-and-remove-attachments-to-an-item-in-a-compose-form

Answer 1

If you are trying to attach a local file from the user's PC to the email then unfortunately you cannot do so since of course this is JavaScript. The attachment methods in the Outlook Add-in API can only deal with web-based files. You would need a web form or other mechanism to upload the file to your web service to an accessible URI location which you can then point to with the addFileAttachmentAsync method. The ASP.NET Web API would be one alternative to implement your web service in.

Answer 2

In addFileAttachmentAsync the attachmentURI parameter is sent to the Server (in OWA's case), or to the Outlook App (desktop Outlook). Then, either the Server or Outlook goes and downloads the file, and attaches it to the e-mail. If OWA/Outlook can't reach the URI that you provide, then it won't work.