You must disable cookie detection.
Safari underwent a change and no longer allows cookies to be sent in an iFrame for another site. Cookies are what’s used to pass through and authenticate a user for our SSOs. This will impact any user attempting to access SSOs via Safari. To eliminate this problem, you can use a different internet browser or, if you wish to continue using Safari, follow the steps below.
Step 1. Within the Safari menu, click “preferences” and navigate to the “privacy” tab across the modal that pops up.
Step 2. Make sure “Block all cookies” is unchecked.
Below is a screenshot.