WebViewOnNavigating method

DropboxService.cs

        private async void WebViewOnNavigating(object sender, WebNavigatingEventArgs e)
        {
            if (!e.Url.StartsWith(RedirectUri, StringComparison.OrdinalIgnoreCase))
            {
                // we need to ignore all navigation that isn't to the redirect uri.
                return;
            }

            try
            {
                var result = DropboxOAuth2Helper.ParseTokenFragment(new Uri(e.Url));

                if (result.State != this.oauth2State)
                {
                    return;
                }

                this.AccessToken = result.AccessToken;

                await SaveDropboxToken(this.AccessToken);
                this.OnAuthenticated?.Invoke();
            }
            catch (ArgumentException)
            {
                // There was an error in the URI passed to ParseTokenFragment
            }
            finally
            {
                e.Cancel = true;
                await Application.Current.MainPage.Navigation.PopModalAsync();
            }
        }