Not getting refresh token from Salesforce

Question

I have been using Force.com Toolkit for .NET for long time. Recently one of a client has started complaining for session invalid issue. So I started digging up and found that I have to refresh token by calling TokenRefreshAsync for which I need to pass on refresh token which I get during authentication. But I am getting null refresh token from SF.

I have tried everything possible thing I found on the internet without any success. Perform requests on your behalf at any time (refresh_token, offline_access) is added in OAuth Scopes:

Refresh token expiry is set at 2 days:

This is the simple code I am using to authenticate:

var task = authClient.UsernamePasswordAsync(consumerKey, consumerSecret, username, password, callback);
task.Wait();

What am I missing here?

Answer 1

The Username-Password Oauth Flow does not provide a refresh token on Salesforce, regardless of scopes:

This OAuth authentication flow passes the user's credentials back and forth. Use this authentication flow only when necessary. No refresh token is issued.

If you want a refresh token, you'll need to implement a different OAuth flow (preferable!), or eschew the refresh token and reauthenticate when your access token expires. The latter makes you vulnerable to credential and security token changes on the part of the authenticated user, however, which using a more suitable OAuth flow grants resilience against.