SharePoint Online CSOM The remote server returned an error: (401) Unauthorized

Hi there

Don't seem to be getting anywhere with this, i'm trying to use CSOM to download and resize an image file. Sound simple enough but i seem to be having permission issue. Keep getting The remote server returned an error: (401) Unauthorized

My code looks like this:

using (ClientContext clientContext = TokenHelper.CreateRemoteEventReceiverClientContext(properties))
            {
                if (clientContext != null)
                {
                    try
                    {
                        clientContext.Credentials = new NetworkCredential("username", "password", "domain");

I also tried to use App only credentials like this but no luck:

Uri siteUri = new Uri(contextClient.Url);

                string realm = TokenHelper.GetRealmFromTargetUrl(siteUri);

                //Get the Access token from the URL
                //Requires this app to be registered with the tenant
                string accessToken = TokenHelper.GetAppOnlyAccessToken(TokenHelper.SharePointPrincipal, siteUri.Authority, realm).AccessToken;

The permission is blows up here on this line: 

FileInformation fileInfo = Microsoft.SharePoint.Client.File.OpenBinaryDirect(clientContext, fileRef);

Any help will be appreciated.