If I take content that's posted on Stack Exchange (or, more generically, from a site that publishes user content based on a CC BY-SA license) and re-use it elsewhere, who is my license from? Is it the author themselves, or is it from Stack Exchange (from the publishing site)?
Relatedly, who has the authority to request that attribution be removed? CC BY-SA provides for the licensor to request attribution be removed, but who has to make that request in this case?