How to prevent saving browser pages in activity stack history

Question

1. User click one button on Activity#1 to start Activity#2.
2. One button on Activity#2 start system default browser(Intent.ACTION_VIEW) to get Twitter authorized.
3. After user allow, Twitter redirect user to Activity#2(Custom intent-filter+data) and it save the tokens.

Now, if I press back key, the app back to browser, how to prevent this and return to Activity#1? Try several Intent.Flag before start browser with no luck.

Thanks.