Sets up OAuth providers to work with portless local dev URLs by switching from rejected .localhost subdomains to valid TLDs like .dev or .app. Google and Apple are the main culprits here, they reject .localhost in redirect URIs even though they allow bare localhost. The skill walks through configuring Google, Apple, Microsoft, Facebook, and GitHub with the right callback URLs, plus how to set NEXTAUTH_URL and similar vars so your auth library constructs URLs correctly. If you've ever hit "redirect_uri_mismatch" during local OAuth testing, this is the fix. Includes a table showing exactly which providers block what, which is honestly useful reference material on its own.
npx skills add https://github.com/vercel-labs/portless --skill oauth