dedicated https subdomain for login and admin area

Hello,
I have a WordPress network with domain mapping.
I have an only subdomain with ssl valid certificate : https://ssl.1twitif.fr/
I don’t use it only for wordpress so admin page must be accessible in a subfolder : https://ssl.1twitif.fr/wp/wp-admin/ for exemple.

my website front-ends are in http only :
https://www.1twitif.fr/
https://1dex.fr/
and some other.

I’ve made somes test moving my main network site :
https://wp.1twitif.fr/
or :
https://ssl.1twitif.fr/wp/

In the first case my admin is not here : https://ssl.1twitif.fr/wp/wp-admin/ and not in https. but anything else work fine.

In the second case, my admin is running at right place, with https, but I have infinit loop, error 500 and execive slow trouble in all frontend.

Is there a good way to make my stuff work as i would like it work ?
Is there any way i can use to make my stuff work as i would like it work ?

Thank your for your help,
regards,
GammaNu