I understand that CAs issue certificates based on common names (CNs) like www.amazon.com and that certs are not based on URLs like www.amazon.com/stuff.
How is it that when I go to www.amazon.com, it is not secured and when I press Log In, the connection is now SSL-secured? I could understand if the login link redirected me to a site like login.amazon.com where there was an SSL cert for the sub-domain... But the login page on Amazon starts with www.amazon.com which is not secured when you go to it without logging in.
This is the exact login link: