Facebook and other sites have features where they ask users for their credentials for 3rd party web sites (see image below). Presumably, facebook then uses the credentials to login as the user and harvest their email contacts to match against facebook's user database.
Does anyone know that kind of permission is required from a 3rd party website to login on behalf of one of their users? Or is no permission required?
I suppose it is analogous to giving an apartment key to your pet sitter. The only thing that would stop the pet sitter from entering your apartment is if the complex's TOS explicitly state that no one may unlock the door of an apartment that they do not own. But would those TOS apply to the pet sitter? Or would they only apply to renters who enter into a service agreement with the complex?