How do I get Azure AD OAuth2 Access Token and Refresh token for Daemon or Server to C# ASP.NET Web API

I have implemented an Azure AD OAuth2 Daemon or Server to ASP.NET Web API. However I only receive an access token which is the property on the AuthenticationResult. See implementation below.

    public IHttpActionResult GetAccessToken(string clientId, string clientkey)
    {
        AuthenticationContext authContext = new AuthenticationContext(authority);
        ClientCredential clientCredential = new ClientCredential(clientId, clientkey);
        AuthenticationResult authenticationResult = authContext.AcquireTokenAsync(resourceUri, clientCredential).Result;
        Authorisation authorisation = new Authorisation {access_token = authenticationResult.AccessToken,
                                                token_type = authenticationResult.AccessTokenType,
                                                expires_on = authenticationResult.ExpiresOn };

        return Ok(authorisation);
    }   

This returns only access token. I would like an implementation, a Daemon or Server implementation that returns both access token and refresh token. Have your seen or done similar implementation. Any useful links to an example are welcome.