Can't get better-auth working with the Tanstack Start and Convex stack

import { createFileRoute } from '@tanstack/solid-router'

const convexSiteUrl =
  import.meta.env.PUBLIC_CONVEX_SITE_URL! ||
  process.env.PUBLIC_CONVEX_SITE_URL! ||
  import.meta.env.VITE_CONVEX_SITE_URL! ||
  process.env.VITE_CONVEX_SITE_URL!

async function handler({ request }: { request: Request }) {
  try {
    const requestUrl = new URL(request.url)

    if (!convexSiteUrl) {
      throw new Error('VITE_CONVEX_SITE_URL is not set')
    }
    const nextUrl = `${convexSiteUrl}${requestUrl.pathname}${requestUrl.search}`

    const newRequest = new Request(request, { redirect: 'manual' })
    newRequest.headers.set('accept-encoding', 'application/json')

    const response = await fetch(nextUrl, newRequest)

    const body = response.body
    const status = response.status
    const statusText = response.statusText

    const headers = new Headers(response.headers)

    // Ensure no caching
    headers.set('Cache-Control', 'no-cache, no-store, must-revalidate')
    headers.set('Pragma', 'no-cache')
    headers.set('Expires', '0')

    return new Response(body, {
      status,
      statusText,
      headers,
    })
  } catch (e: any) {
    console.error(e)

    let message = 'Internal Server Error'

    if (import.meta.env.MODE !== 'production') {
      message = e?.message || message
    }

    return new Response(message, { status: 500 })
  }
}

export const Route = createFileRoute('/api/auth/$')({
  server: {
    handlers: {
      GET: handler,
      POST: handler,
    },
  },
})

import { createFileRoute } from '@tanstack/solid-router'

const convexSiteUrl =
  import.meta.env.PUBLIC_CONVEX_SITE_URL! ||
  process.env.PUBLIC_CONVEX_SITE_URL! ||
  import.meta.env.VITE_CONVEX_SITE_URL! ||
  process.env.VITE_CONVEX_SITE_URL!

async function handler({ request }: { request: Request }) {
  try {
    const requestUrl = new URL(request.url)

    if (!convexSiteUrl) {
      throw new Error('VITE_CONVEX_SITE_URL is not set')
    }
    const nextUrl = `${convexSiteUrl}${requestUrl.pathname}${requestUrl.search}`

    const newRequest = new Request(request, { redirect: 'manual' })
    newRequest.headers.set('accept-encoding', 'application/json')

    const response = await fetch(nextUrl, newRequest)

    const body = response.body
    const status = response.status
    const statusText = response.statusText

    const headers = new Headers(response.headers)

    // Ensure no caching
    headers.set('Cache-Control', 'no-cache, no-store, must-revalidate')
    headers.set('Pragma', 'no-cache')
    headers.set('Expires', '0')

    return new Response(body, {
      status,
      statusText,
      headers,
    })
  } catch (e: any) {
    console.error(e)

    let message = 'Internal Server Error'

    if (import.meta.env.MODE !== 'production') {
      message = e?.message || message
    }

    return new Response(message, { status: 500 })
  }
}

export const Route = createFileRoute('/api/auth/$')({
  server: {
    handlers: {
      GET: handler,
      POST: handler,
    },
  },
})