(401) Unauthorized exception while downloading file from SharePoint

Question

I have generated an access token using OAuth mechanism for SharePoint Online server. I am using this token to create ClientContext using CSOM. While I am able to access all the sites, libraries, and folders seamlessly, I get error

The remote server returned an error: (401) Unauthorized.

while downloading the file from SharePoint Online. Below is the code that I am using for file download:

var clientContext = TokenHelper.GetClientContextWithAccessToken("https://adventurer.sharepoint.com/Subsite1", accessToken);
var list = clientContext.Web.Lists.GetByTitle("SubSite 1 Library 1");
string vquery = @"<View Scope='RecursiveAll'><Query><Where><Eq><FieldRef Name='UniqueId' /><Value Type='Lookup'>" + "6718053d-a785-489c-877f-5a4b88dcb2a7" + "</Value></Eq></Where></Query></View>";
CamlQuery query = new CamlQuery();
query.ViewXml = vquery;
var listItems = list.GetItems(query);
clientContext.Load(listItems, items => items.Take(1).Include(item => item.File));
clientContext.ExecuteQuery();

var fileRef = listItems[0].File.ServerRelativeUrl;
var fileInfo = Microsoft.SharePoint.Client.File.OpenBinaryDirect(clientContext, fileRef);

I don't understand the root cause of this error, as I am passing client context with right access token. I want to know if OpenBinaryDirect has a limitation to work with access tokens? If not, what is wrong with above code? Is there any other alternative that can be used to download using access token?

Answer 1

After trying a lot of alternatives, I have come to conclusion that OpenBinaryDirect() cannot be used with OAuth tokens. I was able to download file from SharePoint Online using two other approaches. I am posting the answers here so that it might help someone:

Approach 1 (OpenBinaryStream):

var file = clientContext.Web.GetFileByServerRelativeUrl(fileRef);
clientContext.Load(file);
clientContext.ExecuteQuery();                    
ClientResult<Stream> streamResult = file.OpenBinaryStream();
clientContext.ExecuteQuery();

While this approach works perfectly, OpenBinaryStream is not available in Microsoft.SharePoint.Client.dll <= v 14.0.0.0.

Approach 2 (WebClient or Other Http Requests):

string downloadUrl = HostURL + "/_api/web/getfilebyserverrelativeurl('" + fileRef + "')/$value";
WebClient client = new WebClient(); 
client.Headers.Add("Authorization", "Bearer " + accessToken);
client.DownloadFile(downloadUrl, filePath);

Note the download URL that I have used for WebClient. Normal file URL will not work to download files from SharePoint Online.