safe-action-better-auth — Claude Code skill: auth for safe actions

What safe-action-better-auth does

Reach for it when a Next.js project already uses next-safe-action and you are adding sign-in or permission checks to server actions. The skill walks through building an action client with the betterAuth(auth) middleware: it calls auth.api.getSession() with headers from next/headers, and when there is no session it triggers unauthorized() from next/navigation. Your action context gets { auth: { user, session } }, with types inferred from your Better Auth instance, plugin fields included.

The steps cover a Better Auth instance with nextCookies() last in the plugin array, the authInterrupts: true flag in next.config.ts, a separate client for authenticated actions, and a sample action with inputSchema. There is a section on custom authorize callbacks plus the BetterAuthContext, AuthorizeFn and BetterAuthOpts types.

Two spots where things break quietly. Skip nextCookies() and the session comes back null whenever an action tries to set cookies, so check the plugin order first. Skip the authInterrupts flag and unauthorized() throws at runtime. Also, don't refetch the session inside authorize — it arrives as authData.