We have a site, example.com, that includes a login system for the end users.
We then have a CMS, cms.example.com, in which admin users log in to edit the content of the main site.
Both sites are treated as separate projects, with independent login systems and different front ends, because we want to give the users different UXs.
We're considering migrating the CMS to its own domain, something like cmsexample.com.
The reasong behind it is that we think the web is moving towards treating a domain always as a single entity, without distinction of subdomains, for the sake of clarity and transparency towards the end user.
- Browser behaviour: logging into cms.example.com will trigger the following message on Firefox and IE: "Would you like to store your password for example.com?".
- Firefox, IE and Opera highlight the domain name on the URLs, ie they consider the subdomain a less important part of the URL: cms.example.com/path/to/file
- On www.facebook.com, users get seamlessly redirected to apps.facebook.com when using an app.
- Google takes users from mail.google.com to accounts.google.com for authentication, and then back to mail.google.com once they are logged in.
But there is also a large number of counterexamples, including this very same site ux.stackexchange.com, blogs and personal sites hosted on many blogging platforms, or custom sites like companyname.mainproduct.com.
In a nutshell then, the question is: Do two different login systems on cmsexample.com / example.com provide a better user experience than if they are on cms.example.com / example.com ?