How do you deal with the url if it can change?
For example, you register for example.com on http://register.example.com and then login on https://login.example.com and in the future they may change it to https://examplelogin.com/auth/
Or what if the company changes name? For example, I used to log into my bank on http://wamu.com and now they are bought by Chase so it's http://chase.com