Passkeys are a replacement for passwords that use public/private cryptographic key pairs for login in a way that can be more user-friendly and resistant to a number of kinds of attacks. Let’s implement account registration and login with passkeys in a simple Phoenix web app.

This work is heavily based on this article by Adam Langley, which provides a great deal of information about implementing passkeys. My goal here is to fill in some more of the details, and provide some Elixir-specific information. As with Adam’s article, I’m not going to use any WebAuthn libraries (even though that may be advisable from a security/maintenance perspective) since I think it’s interesting and helpful to understand how things actually work.

Providing an exhaustive, production-ready implementation is a non-goal of this post. I’m going to make some slightly odd decisions for pedagogical reasons, and leave some things incomplete. That said, I’ll try to note when I’m doing so.

I’m very excited for the project I’ve been working on all year to finally be public. LiveView Native is a library that lets you build native apps backed by Phoenix LiveView. I’ve been developing the iOS client which is backed by SwiftUI.

Using LiveView Native lets you avoid duplicating business logic on the frontend and save time on implementing dedicated APIs for native apps. The iOS client can be integrated into any existing app by using a single SwiftUI view, so it’s easy to adopt it for just a single screen at a time.

You can find the documentation^[1] for the Swift package here, including a step-by-step tutorial which walks you through building a complete app with LiveView Native.

We’ve also developed a simple chat app which was used by the attendees of ElixirConf this year, and serves as a complete example of a LiveView Native app.

I’m very excited to see what people build with it.

Armed with the ID3 decoder from my last post, we can extract most of the metadata from MP3 files. However, the one piece I still want for my music cataloging software is the track duration, which, for the vast majority of my files, is not included in the ID3 tag. Getting the duration of an audio file isn’t as straightforward as I had hoped. One of the easiest solutions would be to just shell out to another piece of software, such as ffmpeg, which can handle a great many audio formats. But that would be boring, and I wanted to minimize the number of dependencies, which meant writing a rudimentary MP3 decoder myself. Luckily, I don’t need to actually playback audio myself, so I can avoid a great deal of complexity. I only need to parse enough of the MP3 file to figure out how long it is.

On and off for the past year and a half or so, I’ve been working on a small side project to catalog and organize my music library, which is predominantly composed of MP3 files^[1]. There are existing pieces of software out there that will do this (such as Beets and Airsonic), but, as many a programmer will attest to, sometimes it’s just more fun to build your own. The choice of language was easy. For a couple years now, Elixir has been my favorite for any back-end web dev. I also had an inkling that its powerful pattern matching facilities could work on arbitrary binary data—perfect for parsing file formats.

I knew that MP3 files had some embedded metadata, only for the reason that looking at most tracks in Finder shows album artwork and information about the track. Cursory googling led me to the ID3 spec.

About a year ago, I set out to learn the Elixir programming language. At the time, it was mainly so I could contribute to Pleroma, but I’ve since fallen in love with the language.