This project uses SimpleAuth. But since SimpleAuth is 3-4 years old and the dependencies are broken, I have created this project. You just need to drag and drop all the files from the SimpleAuth folder to your project and make sure to mark "copy items if needed".
For Swift 3/4 you need to create a Bridging Header or simply use mine.
Add the Header as Bridging Header at the Target's Build Settings.
For further explanation please read:
http://stackoverflow.com/questions/40286744/oauth2-swift-3-instagram/40373964#40373964