// Also you can use your own client configuration.
var auth = new GoogleAuth()
{
  clientId = "...",
  redirectUrl = "...",
  scope = "openid email profile"
};

using var authenticationSession = new AuthenticationSession(auth, new StandaloneBrowser());

var crossPlatformBrowser = new CrossPlatformBrowser();
var crossPlatformBrowser.platformBrowsers.Add(RuntimePlatform.WindowsEditor, new StandaloneBrowser());
var crossPlatformBrowser.platformBrowsers.Add(RuntimePlatform.WindowsPlayer, new StandaloneBrowser());
var crossPlatformBrowser.platformBrowsers.Add(RuntimePlatform.OSXEditor, new StandaloneBrowser());
var crossPlatformBrowser.platformBrowsers.Add(RuntimePlatform.OSXPlayer, new StandaloneBrowser());
var crossPlatformBrowser.platformBrowsers.Add(RuntimePlatform.IPhonePlayer, new ASWebAuthenticationSessionBrowser());

using var authenticationSession = new AuthenticationSession(auth, crossPlatformBrowser);

// Opens a browser to log user in
AccessTokenResponse accessTokenResponse = await authenticationSession.AuthenticateAsync();

// Authentication header can be used to make authorized http calls.
AuthenticationHeaderValue authenticationHeader = accessTokenResponse.GetAuthenticationHeader();

// Gets the current acccess token, or refreshes if it is expired.
accessTokenResponse = await authenticationSession.GetOrRefreshTokenAsync();

// Gets new access token by using the refresh token.
AccessTokenResponse newAccessTokenResponse = await authenticationSession.RefreshTokenAsync();

// Or you can get new access token with specified refresh token (i.e. stored on the local disk to prevent multiple sign-in for each app launch)
newAccessTokenResponse = await authenticationSession.RefreshTokenAsync("my_refresh_token");