Incorrect X-Forwarded-Proto header

[alphabeat]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 22.5.0: Thu Jun  8 22:22:19 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T8103
Binaries:
  Node: 16.20.0
  npm: 8.19.4
  Yarn: 1.22.19
  pnpm: N/A
Relevant packages:
  next: 13.4.7
  eslint-config-next: 13.4.7
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 4.9.5

Which area(s) of Next.js are affected? (leave empty if unsure)

No response

Link to the code that reproduces this issue or a replay of the bug

https://github.com/alphabeat/infinite-loop-middleware

To Reproduce

Use this middleware on a production environment:

import { NextRequest, NextResponse } from 'next/server';

export function middleware(req: NextRequest) {
    if (process.env.NODE_ENV === 'production' && req.headers.get('x-forwarded-proto') !== 'https') {
        return NextResponse.redirect(`https://${req.headers.get('host')}${req.nextUrl.pathname}`, 301);
    }

    return NextResponse.next();
}

Describe the Bug

The X-Forwarded-Proto header never equals https as expected: nextjs returns http,http or https,http. This creates an infinite loop and ends up with an ERR_TOO_MANY_REDIRECTS error on production.

Expected Behavior

The X-Forwarded-Proto header should either return http or https as described on the MDN docs: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-Proto

Which browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

Heroku

[alphabeat]

Related discussion: #51970

[MattElcock]

We're getting the same issue. Our logs:

x-forwarded-for: ::1,::ffff:127.0.0.1
x-forwarded-port: 3000,3000
x-forwarded-proto: http,http
x-forwarded-host: localhost:3000

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.