fix login in migration page

In the migration page, there is an authentication check to allow user to login. However, the Migration_Extract_Action requires login by default.

Since the check was done before authentication check, this causes an authentication failure whether the username and password is correct or not.

Making login not required by Migration_Extract_Action will allow the authentication.

This commit also fixes the login issue for Migration_Extract_Action since there are something missing in the $_SESSION