Access denied when downloading file from Sharepoint CSOM

Question

I am trying to download a file from a client Sharepoint site. I am using sharepoint CSOM.

My code is as follows:

using Microsoft.SharePoint.Client;

var username = "username";
var password = "pass";

var url = "https://myclient.sharepoint.com/";
var fileurl = "https://myclient.sharepoint.com/teams/folder1/folder%20x/somefile.docx";
using (ClientContext context = new ClientContext(url))
{    
    SecureString passWord = new SecureString();
    foreach (char c in password.ToCharArray()) passWord.AppendChar(c);
    context.Credentials = new SharePointOnlineCredentials(username, passWord);

    Uri filename = new Uri(fileurl);
    string server = filename.AbsoluteUri.Replace(filename.AbsolutePath, "");
    string serverrelative = filename.AbsolutePath;

    Microsoft.SharePoint.Client.File file = context.Web.GetFileByServerRelativeUrl(serverrelative);
    context.Load(file);
    ClientResult<Stream> streamResult = file.OpenBinaryStream();
    context.ExecuteQuery();
    var file2 = streamResult.Value;
}

The problem is that I get access denied, yet when I log in with the same credentials, I can download the file successfully.

• Is there a separate permission in Sharepoint for downloading file from API instead of UI?
• Could the space in the folder name be the problem?

UPDATE

Verified this does not have anything to do with spaces in folder or filename.

Answer 1

In case if SharePoint site uses multiple authentication providers using a set of Windows credentials (also relevant for SharePoint Online), the additional header must be included in a request: X-FORMS_BASED_AUTH_ACCEPTED with a value of f

For ClientContext class the header could be included like this:

ctx.ExecutingWebRequest += (sender, e) =>
{
    e.WebRequestExecutor.WebRequest.Headers["X-FORMS_BASED_AUTH_ACCEPTED"] = "f";
};

Example

var file = ctx.Web.GetFileByUrl(fileAbsUrl);
ctx.Load(file);
var streamResult = file.OpenBinaryStream();
ctx.ExecuteQuery();


//save into file
using (var fileStream = System.IO.File.Create(@"C:\path\filename.docx"))
{
   streamResult.Value.Seek(0, SeekOrigin.Begin);
   streamResult.Value.CopyTo(fileStream);
}

Note: instead of converting to relative url, GetFileByUrl method is used which accepts absolute url

Answer 2

Problem was that I was not connecting to the right url ( new ClientContext(url) )

I was connecting to: https://myclient.sharepoint.com/

I should have been connecting to: https://myclient.sharepoint.com/teams/folder1/