When a user clicks on "Get credentials", a new window appears
where users can authenticate themselves. It is a remote window
implementing whatever mechanism the target cloud implements.

When the authentication window opens, the "Get credentials"
button disappears.

After the authentication is complete or canceled, the following
operations take place synchronously and the order they appear
bellow:
- if the authentication window is open, close it
- remove all cookies related to the account and pithos UI URLs
- Reactivate the "Get credentials" button.