Byte order marks on challenge response

ytechie

I set up a Node.js server to respond to the API challange request for a webhook. I can't seem to get it to accept the challenge. I can't tell if it's appending byte order marks, or if Node.js is secretly sending them. I masked out some of the info below, but I kept the key parts.

 

Notice the extra "\xef\xbb\xbf" prepended to the challenge response.

 

Error: Incorrect response to challenge. We didn't receive the expected response xxxxx. See the actual response body we received below.

Request:
GET http://xxxx.ngrok.io/api/DropboxWebhook?challenge=xxxxx

Response:
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Server: Microsoft-HTTPAPI/2.0
Connection: keep-alive
Date: Wed, 28 Dec 2016 18:10:30 GMT
Content-Type: text/plain; charset=utf-8

Response Body (First 256 bytes):
\xef\xbb\xbfxxxxx

ytechie

It was an issue specific to Azure Functions. The fix was to use a content type of "application/octet-stream".

 

Here is code that I confirmed works with dropbox:

res = {
            body: challenge,
            headers: {
                'Content-Type': 'application/octet-stream'
            }
        };