The App Store should have worked this way since day 1.

From Jay Peters at The Verge:

Apple Cannot:

  • Impose “any commission or any fee on purchases that consumers make outside an app”
  • Restrict developers’ style, formatting, or placement of links for purchases outside of an app
  • Block or limit the “use of buttons or other calls to action”
  • Interfere with consumers’ choice to leave an app with anything beyond “a neutral message apprising users that they are going to a third-party site”