logging in with different user / resource owner - oauth-2.0

Question

i am trying to write a tool that creates entries in the google calendar.
after following the google docs and creating an client-identifier/secret in the api console, i managed to put together a client that authenticates correctly and shows my registered google calendars. right now for me it looks like my google-account is somehow tied to my client-identifier/secret. what i want to know is: how can i change the auth process so that it is possible for an other user of this tool to enter his google-id and get access to his calendars?
EDIT: in other words (used in the RFC): I want make the resource owner-part editable while leaving the client-part unchanged. but my example, although working, ties together client and resource owner.
here is my app that works fine so far:
public void Connect()
{
var provider = new NativeApplicationClient(GoogleAuthenticationServer.Description);
provider.ClientIdentifier = "123456123456.apps.googleusercontent.com";
provider.ClientSecret = "nASdjKlhnaxEkasDhhdfLklr";
var auth = new OAuth2Authenticator<NativeApplicationClient>(provider, GetAuthorization);
var service = new CalendarService(auth);
//Events instances = service.Events.Instances("primary", "recurringEventId").Fetch();
var list = service.CalendarList.List().Fetch();
foreach (var itm in list.Items)
Console.WriteLine(itm.Summary);
}
private static readonly byte[] AditionalEntropy = { 1, 2, 3, 4, 5 };
private static IAuthorizationState GetAuthorization(NativeApplicationClient arg)
{
var state = new AuthorizationState(new[] { CalendarService.Scopes.Calendar.GetStringValue() });
state.Callback = new Uri(NativeApplicationClient.OutOfBandCallbackUrl);
var refreshToken = LoadRefreshToken();
if (!String.IsNullOrWhiteSpace(refreshToken))
{
state.RefreshToken = refreshToken;
if (arg.RefreshToken(state))
return state;
}
var authUri = arg.RequestUserAuthorization(state);
// Request authorization from the user (by opening a browser window):
Process.Start(authUri.ToString());
var frm = new FormAuthCodeInput();
frm.ShowDialog();
// Retrieve the access token by using the authorization code:
var auth = arg.ProcessUserAuthorization(frm.txtAuthCode.Text, state);
StoreRefreshToken(state);
return auth;
}
private static string LoadRefreshToken()
{
try
{
return Encoding.Unicode.GetString(ProtectedData.Unprotect(Convert.FromBase64String(Properties.Settings.Default.RefreshToken), AditionalEntropy, DataProtectionScope.CurrentUser));
}
catch
{
return null;
}
}
private static void StoreRefreshToken(IAuthorizationState state)
{
Properties.Settings.Default.RefreshToken = Convert.ToBase64String(ProtectedData.Protect(Encoding.Unicode.GetBytes(state.RefreshToken), AditionalEntropy, DataProtectionScope.CurrentUser));
Properties.Settings.Default.Save();
}

Answer 1

Prompt the user to enter their ClientIdentifier and ClientSecret, then pass these values to your Connect method.

Answer 2

i solved the problem myself.
the problem was, that i'm usually always connected to google and because i did't log out from google before my app redirected to google to get the access-token, google automatically generated the access-token for my account - skipping the part where an input-form appears where anyone could enter his/her user-credentials to let google generate an access-token for his/her account.