Allow partitioned cookies

[privacycg]

Allow partitioned cookies

[othermaciej]

I think for WebKit, we'd be more comfortable with just blocking all third-party cookies. Partitioned storage is dangerous in combination with Storage Access API, unless it's made ephemeral. But ephemeral storage doesn't have that much advantage over local variables in JavaScript.

[michael-oneill]

I forgot to say that __k2 cookies would always be partitioned,

[michael-oneill]

I think for WebKit, we'd be more comfortable with just blocking all third-party cookies. Partitioned storage is dangerous in combination with Storage Access API, unless it's made ephemeral. But ephemeral storage doesn't have that much advantage over local variables in JavaScript.

Partitioned cookies can always be simulated via postmessage,sending a first-party cookie value or other origin specific data point, to embedded contexts.

If partitioned cookies are dangerous then so is postMessage and third-party script running in top level context.

The problem with it is its slow, error prone, and opaque.

k2 cookies avoid that because they can be immediately detected, they need a user prompt etc.

They also avoid the postMessage and extra turnround but are more transparent and privacy preserving.

[othermaciej]

Partitioned cookies persist past the point of any frame to the site being opened and perhaps past browser quit (if not ephemeral).

Third-party script running in top level context is indeed dangerous.

[hober]

Forward-duping to #75.