How would use authjs in instrumentation file?

[velvet tapir]

Hi @open bronze. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave:

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You cannot access the authentication session (e.g., via useSession from Auth.js/NextAuth.js) directly inside the instrumentation-client file. The instrumentation-client file runs before React hydration, outside the React component tree, and does not have access to React hooks or context, including authentication state. This is a limitation of the execution environment for instrumentation-client, which is designed for global, pre-hydration setup only and not for per-user or per-session logic see docs.

If you need to identify users in PostHog with their session data, you must do this in a Client Component after authentication is available. For example, you can create a small Client Component that uses useSession and calls posthog.identify when the session is ready:

'use client';

import { useEffect } from 'react';
import { useSession } from 'next-auth/react';
import posthog from 'posthog-js';

export function PostHogIdentify() {
  const { data: session } = useSession();

  useEffect(() => {
    if (session?.user) {
      posthog.identify(session.user.id, {
        email: session.user.email,
        name: session.user.name,
        // add other properties as needed
      });
    }
  }, [session]);
}

Then, include this component in your layout or wherever it will be mounted after authentication is available.

Summary:

• The instrumentation-client file cannot access per-user session data or React hooks.
• User identification for analytics must be done in a Client Component after authentication is available see docs.

If you need to initialize PostHog as early as possible, do so in instrumentation-client, but defer user identification to a Client Component after session data is available.

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