What even is code signing in iOS? (Runway)

If you have been developing for iOS for a while, chances are you had one of two issues involving code signing, the process where Apple/Xcode forces you to "sign" your app with a developer certificate in order to be able to archive it and submit it to the App Store.

I find code signing to be interesting not just because of what it does, but because it's one of those things that iOS developers kinda just take for granted. We know it's there and we know how to deal with it, but we don't really stop to think why it's there or what it's doing under the hood. We just follow Apple's convoluted steps on how to make it work and move on with our lives.

In practice, code signing is an incredibly important safety feature of Apple's ecosystems. Knowing what it is and why it exists makes debugging issues related to it considerably easier, so I've written this article to help you understand it.