Use of headers() in next 15 give a error

[ncasola]

Describe the bug

Use of headers() in next 15 give a error:
[ Server ] Error: Route "/private" used headers().get('X-FiefAuth-Access-Token-Info'). headers() should be awaited before using its value. Learn more: https://nextjs.org/docs/messages/sync-dynamic-apis

To Reproduce

Follow the integrate guide in https://docs.fief.dev/integrate/javascript/ssr/nextjs-app/

Configuration

• JavaScript environment: NextJs 15, pnpm, TS

• Fief client version: npm @/fief latest

• Fief Cloud or self-hosted: self-hosted

• If self-hosted, Fief version: ghcr.io/fief-dev/fief:latest

Additional context

[frankie567]

Thank you for the report @ncasola 🙏

This is a breaking change introduced in Next.js 15... It's really hard to keep up with them, this is exhausting.

[ysnbyzli]

Thank you for the report @ncasola 🙏

This is a breaking change introduced in Next.js 15... It's really hard to keep up with them, this is exhausting.

Hello, I would like to contribute to this issue. Could you guide me on how to proceed?

After reviewing the code, I believe the issue can be resolved by following these steps:
• The function should be converted to an async function, and the const headersList = headers(); line should be awaited.
• The places where the function is used should also be updated to use async/await.

Here is a proposed solution example:

const getServerSideHeaders = async (headerName: string, req?: IncomingMessage): Promise<string | null> => {
  // "Legacy" Next.js, req object is required
  if (req) {
    return req.headers[headerName.toLowerCase()] as string | null;
  }
  // Next.js 15 style
  const headersList = await headers();
  return headersList.get(headerName);
};

This way, the headers() function will be handled asynchronously, and values will be retrieved correctly. Could you assist me with this?