This idea https://success.salesforce.com/ideaView?id=08730000000BqQmAAK requesting the ability to be able to define a custom login page (e.g. with you own branding) is marked as "delivered" but with no link to what was actually delivered.
But there is still activity on this thread http://brianpeddle.com/2011/06/06/building-a-custom-salesforce-login/ that dates from 2011.
What is the best way to create a custom login page (for a standard "salesforce" or "salesforce platform" licensed user that logs in to the normal salesforce pages i.e. not sites) today?