protected override Uri GetServiceLoginUrl(Uri returnUrl)
{
var builder = new UriBuilder(_authorizationEndpoint);
builder.AppendQueryArgs(
new Dictionary<string, string>
{
{"response_type", "code"},
{"redirect_uri", returnUrl.AbsoluteUri},
{"scope", "https://www.googleapis.com/auth/userinfo.email"},
{"client_id", _clientId}
});
return builder.Uri;
}