Cookies not getting clear in In-App browser for mobile

.We are trying to authenticate the user for the Mobile app with global authentication. In the process, we access the Global auth login page in an In-App browser which as a result performs the authentication process. Along similar lines, for logging out the user, the logout URL is opened in an in-app browser.

In our mobile we are not using cookies but Third party login app maintaining cookies for logout. if we are trying to logout in In-App browser cookies are not getting clear, because of that we are not able to logout from the page. is this because of In-app browser any solution to clear cookies on logout