How to create a log in and registration page on a sub-domain?

Hello,

I want to allow users to log in and register on a sub-domain (login.mydomain.com or my.mydomain.com) instead of going through mydomain.com/wp-admin.

This should allow users to be logged in a network or multisite i.e be logged in wiki.mydomain.com (wiki pro plugin), market.mydomain.com (marketpress plugin) and jobs.mydomain.com (Jobs and expert plugin)

Also allow users to gain access to wordpress dashboard (I'll be using easy blogging plugin) to post.

I don't want users to log in or register through mydomain.com/wp-admin.

P.S If you have any links to help me that would be awesome.

Thank You