I am using a web app that is running under origin A. To that website, I add an iframe that runs under origin B. Inside that iframe, I would like to embed an image from origin A that requires an authentication cookie to load. I have control over the web app running in the iframe under origin B, but I do not have control over origin A (other than being able to add an iframe to it).
If I disable third-party cookies in Chrome, the authentication cookie is not sent when loading the image, so the image does not load. It seems that Chrome is considering the authentication cookie a third-party cookie, even though it is a first-party cookie that is used by a third-party iframe.
The internet says that Safari is blocking all third-party cookies. However, when I open the page in Safari, the image loads successfully.
Why is this the case? Does Safari not consider the cookie third-party? Or does Safari in fact not block all third-party cookies? Where can I find more information about this?