BA
Better Auth•12mo ago
Jackson Kasi

Error with Immutable Headers in Better Auth Session Middleware on Deno Server

Guys Hello , I’m working on setting up session management using Better Auth with a Deno server and Hono as the framework. I followed the documentation to create a middleware for session handling, but I'm running into an issue when trying to retrieve sessions. Here’s a simplified version of my code: 
import { type Context, type Next } from "@hono/hono";
import { auth } from "../auth.ts"; // Import Better Auth instance

export const sessionMiddleware = async (c: Context, next: Next) => {
  try {
    var headers = c.req.raw.headers;
    // @ts-ignore
    const session = await auth.api.getSession({ headers });

    if (!session) {
      c.set("user", null);
      c.set("session", null);
      return next();
    }

    c.set("user", session.user);
    c.set("session", session.session);
    return next();
  } catch (error) {
    console.error("Error in sessionMiddleware:", error);
    // Return a 500 response if an error occurs
    return c.json({ error: "Failed to retrieve session" }, 500);
  }
};

export default sessionMiddleware;
import { type Context, type Next } from "@hono/hono";
import { auth } from "../auth.ts"; // Import Better Auth instance

export const sessionMiddleware = async (c: Context, next: Next) => {
  try {
    var headers = c.req.raw.headers;
    // @ts-ignore
    const session = await auth.api.getSession({ headers });

    if (!session) {
      c.set("user", null);
      c.set("session", null);
      return next();
    }

    c.set("user", session.user);
    c.set("session", session.session);
    return next();
  } catch (error) {
    console.error("Error in sessionMiddleware:", error);
    // Return a 500 response if an error occurs
    return c.json({ error: "Failed to retrieve session" }, 500);
  }
};

export default sessionMiddleware;
Issue Details Upon running the server, I receive the following error: 
Listening on http://localhost:8087/
Error in sessionMiddleware: TypeError: Cannot change headers: headers are immutable
    at Headers.set (ext:deno_fetch/20_headers.js:425:13)
    at Object.handler (file:///C:/Users/jacks/AppData/Local/deno/npm/registry.npmjs.org/better-auth/0.6.2/dist/plugins.js:1:38396)
    ...
Listening on http://localhost:8087/
Error in sessionMiddleware: TypeError: Cannot change headers: headers are immutable
    at Headers.set (ext:deno_fetch/20_headers.js:425:13)
    at Object.handler (file:///C:/Users/jacks/AppData/Local/deno/npm/registry.npmjs.org/better-auth/0.6.2/dist/plugins.js:1:38396)
    ...
The error occurs when the getSession method is called, indicating that headers are treated as immutable. I attempted the workaround of using raw headers directly from c.req.raw.headers, but this hasn’t resolved the issue. Environment - Deno: 2.0.2 - Better Auth: v0.6.2 - Hono: v4.6.8
No description
3 Replies
Jackson Kasi
Jackson KasiOP•12mo ago
Steps Taken 1. Verified with auth.api.getSession({ headers }) as shown in the documentation. 2. Attempted direct access to raw headers as a possible workaround. Any insights into resolving this immutable headers issue would be greatly appreciated. Thanks for your help! https://www.better-auth.com/docs/integrations/hono
Hono Integration | Better Auth
Hono Integration Guide
Jackson Kasi
Jackson KasiOP•12mo ago
Jackson Kasi
Jackson KasiOP•12mo ago
Hey everyone, I realized my issue with the immutable headers error was a simple oversight. I needed to clone the headers to avoid immutability. Here’s the quick fix: 
// Clone headers to bypass immutability
const headers = new Headers(c.req.raw.headers);
const session = await auth.api.getSession({ headers });
// Clone headers to bypass immutability
const headers = new Headers(c.req.raw.headers);
const session = await auth.api.getSession({ headers });
This small change did the trick! Just sharing in case anyone else runs into the same thing.

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