Why the "401 Unauthorized" when using Call HTTP Web Service against a text file?

Question

I have a mydata.txt file under SiteAssets whose contents are JSON (SharePoint prevented my use of a .json extension). I shared the file with Everyone. I can make a getJSON request with jQuery in the browser to access and read the file's contents. When I attempt to read the file's contents on the back end in SharePoint workflows using Call HTTP Web Service I get a 401.

I was careful to get context info as per: http://blog.appliedis.com/2014/10/09/sharepoint-designer-2013-workflow-working-with-web-services/

I should make the distinction that if I point the Call HTTP Web Service to some list I successfully get the contents of that list. It's only when I point the URL at a flat file that I get the Unauthorized exception so this seems to indicate some particulars with files access.

It made no difference whether I tried to read an .xml or .html file or relocate the file to a Documents library. Access was denied. I can't see as to why a flat file (one that gets periodically updated) couldn't be used as a valid source of information via a REST endpoint.

What am I missing? Why is this at all complicated?

Answer 1

Instead of pointing at /SiteAssets/mydata.txt I pointed at /_api/web/GetFolderByServerRelativeUrl('/SiteAssets')/Files('mydata.txt')/$value and used these headers:

 Accept: application/octet-stream
 Content-Type: application/octet-stream
 X-RequestDigest: <obtained in an earlier request>

I was then able to process the response (which I left as JSON) as a dictionary.

This resource helped:

https://msdn.microsoft.com/en-us/library/office/dn292553.aspx