Unable to get access token to sharepoint online addin using c# Console application

Question

For the past few days, I tried all the ways possible. But couldn't get the access token for accessing Sharepoint online addin using c# console application. However I was able to get the access token from POSTMAN.

I couldn't get any reasonable answer over the internet. I am framing a webrequest and passing the details like Client ID, Client Secret, Tenant, Resource etc similar to framing a POSTMAN request but always getting 401 Unauthorized.

Always getting this message:"The remote server returned an error: (401) Unauthorized."

Answer 1

Try demo in my previous test thread.

App Only Token Issue: Unauthorized access

Uri siteUri = site url;

//Get the realm for the URL
string realm = TokenHelper.GetRealmFromTargetUrl(siteUri);

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

//Get client context with access token
using (var clientContext =
    TokenHelper.GetClientContextWithAccessToken(
        siteUri.ToString(), accessToken))
{
    var web = clientContext.Web;
    var lib = web.Lists.GetByTitle("MyDoc");
    var item = lib.GetItemById(3);
    var file = item.File;
    clientContext.Load(file);
    clientContext.ExecuteQuery();
    Console.WriteLine(file.Name);
    Console.ReadKey();
}