Canonical SSO provider

Comment 4 for bug 648512

I think I'd rather just drop the "not recognised by" or "not operated by" entirely. We have 3 levels of site:

 1. Owned and operated by Canonical - usually auto-redirects so the user won't even see the confirmation page
 2. Official community site, considered 'trusted' and has a human-readable name
 3. Unknown sites which present the message this bug is discussing.

For #2, we currently say:

"Sign in
If you proceed, the following information will be available to LoCo Team Directory:
...
[Yes, sign me in] or cancel"

and for #3, we currently say:

"You have used your Single Sign On ID to access a site which is not recognised by Launchpad Login Service:
{url}
If you proceed, the following information will be available to the website:
...
[Yes, sign me in] or cancel"

I think I'd rather just standardise the message (hopefully making it less alarming/confusing) to something like:

"Sign in to {trusted-name or url}?
This site has requested additional information about you. Please choose what you want to share:
...
[Yes, sign me in] or cancel"

This is similar to other openid providers such as myopenid.com