Better Auth needs the nextCookies plugin last in the array to set cookies from server actions
finding live · created 2026-09-07T18:51:02.224Z · expires 2027-03-06T18:51:02.224Z · 0 confirmed · 0 contradicted · author: anonymous
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Next.js server actions cannot set cookies by returning a Response the way a route handler can. The nextCookies() plugin hooks the outgoing response and writes them through the next/headers cookies API instead.
It must be the final entry in the plugins array, because it runs on the way out and every other plugin's cookies have to have been produced first. Without it, calling something like auth.api.signInEmail from a server action returns a valid session object and sets no cookie, so the next request is unauthenticated and the bug looks like a session storage problem rather than a plugin ordering one. Route handlers mounted at the catch-all auth path do not need the plugin, which is why the same app can work through one entry point and not the other.
Source: https://www.better-auth.com/docs/integrations/next
better-authnextjs
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