Scribbles for my memory

You SSH through a bastion box. So you copied your private key onto it. Now that key lives on one more machine — one more place it can be stolen from, one more copy to rotate when something goes wrong.

SSH agent forwarding removes the need entirely.

What it actually does

This is the part most explanations hand-wave past. Your private key never needed to be on the bastion — that's not how SSH auth works.

• The target machine needs your public key (in ~/.ssh/authorized_keys). It always did.
• The client (you) holds the private key and signs a challenge the target sends.

Without forwarding, when you SSH from the bastion to a third machine, the bastion becomes the client — so it needs the private key to sign. That's the only reason you ever copied it there.

With forwarding, the bastion doesn't sign anything itself. It forwards the challenge back to your agent on your laptop, your agent signs it, and the signature travels back. The bastion never touches the private key.

No forwarding:   laptop (key) → bastion (key) → target (pubkey)
With forwarding: laptop (key+agent) → bastion (no key) → target (pubkey)

Setup

1. Load your key into the agent on your laptop (the agent is usually already running):

ssh-add ~/.ssh/id_rsa

2. Enable forwarding for the bastion in ~/.ssh/config:

Host bastion
    HostName bastion.example.com
    User myuser
    ForwardAgent yes

3. Verify it works:

ssh bastion
ssh-add -l        # lists your keys → forwarding is live
ssh internal-vm   # connects, bastion never had your key

The catch

Only forward through machines you trust. Anyone with root on the bastion can request signatures from your agent while your session is open — effectively borrowing your identity. Never use -A on a shared or untrusted host.

Do you still need it with a passphrase-less key?

If your key has no passphrase and you've already copied it everywhere, forwarding isn't strictly required — direct auth from the bastion works fine. But keep ForwardAgent yes in the config anyway. It costs nothing, and the day you switch to a passphrase-protected key, you'll only ssh-add once on your laptop instead of typing the passphrase on every connection.

If you run gh auth setup-git, the GitHub CLI becomes git's credential helper — and it only ever hands out the token for the active account. The moment you git pull a repo belonging to your other account, you get the wrong token (403, or commits land under the wrong identity). There's no per-repo routing; you'd have to gh auth switch every single time you cross accounts.

You can prove it to yourself — ask the helper for the non-active account and it returns nothing:

"protocol=https`nhost=github.com`nusername=second-account`n`n" |
  & gh auth git-credential get      # exit 1, no token

The fix is to hand git over to Git Credential Manager (it already ships with Git for Windows). GCM picks the token by the username embedded in the remote URL, so routing becomes automatic. gh keeps working for gh issue/gh pr — it uses its own keyring, separate from the git helper.

Switch the helper and point GCM at GitHub:

git config --global --unset-all credential.https://github.com.helper
git config --global credential.helper manager
git config --global credential.https://github.com.provider github
git config --global credential.guiPrompt false   # terminal prompts, no GUI popup on a server

You protect ~/.bashrc.secret with chmod 444 so nothing accidentally overwrites your API keys and passwords. Then your token-refresh script needs to write a new session cookie somewhere — and hits Permission denied.

The fix isn't adding a second writable secrets file. It's stop persisting short-lived tokens entirely.

Refactor the refresh script to output TOKEN HASH on stdout and let the caller capture it:

# refresh_token — reads credentials, prints session token to stdout
CREDENTIALS=$(bash ~/bin/refresh_token 2>/dev/null)
TOKEN=$(echo "$CREDENTIALS" | awk '{print $1}')
HASH=$(echo "$CREDENTIALS" | awk '{print $2}')

No file writes. No second secrets layer. The token lives in the process environment for the duration of the operation and disappears when it's done.

This works because session tokens are cheap to re-obtain — one HTTP call with stored credentials. The only reason to persist them is avoiding that call, which is almost never worth the complexity of managing a writable token store alongside a read-only credential store.

The rule: if you can regenerate it from long-lived credentials in under a second, don't persist it.

If curl throws SSL certificate problem: unable to get local issuer certificate every time in WSL, it's usually a stale CA bundle — especially common on corporate networks running SSL inspection (Zscaler, etc.).

First, refresh the bundle:

sudo apt-get update && sudo apt-get install -y ca-certificates
sudo update-ca-certificates

That fixes most cases. If not, try a full reinstall:

sudo apt-get install --reinstall ca-certificates
sudo update-ca-certificates --fresh

On corporate networks, you likely need your company's root CA certs. You probably already have them somewhere in your Windows filesystem (.crt or .cer files). Copy them all into the trusted store:

sudo cp /c/Certificates/*.crt /usr/local/share/ca-certificates/
sudo cp /c/Certificates/*.cer /usr/local/share/ca-certificates/
sudo update-ca-certificates

Skip .pfx files — those contain private keys and are a different format.

If you don't have the certs handy, export them from Windows:

# PowerShell — list all root certs, look for your company name
Get-ChildItem Cert:\LocalMachine\Root | Select-Object Subject, Issuer | Sort-Object Subject

Or use certmgr.msc (Win+R → certmgr.msc) → Trusted Root Certification Authorities → find your company's cert → right-click → Export → Base-64 encoded X.509.

Test with curl https://google.com after each step.

Most EC2 Windows Server instances don't expose nested virtualization to the guest OS. WSL2 requires Hyper-V extensions, so it simply won't start. WSL1 works fine — it's a translation layer, not a VM.

Enable the WSL feature and reboot in an Admin powershell window:

Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux
Restart-Computer

After reboot, pin the default version to 1:

wsl --set-default-version 1

On Windows Server, Add-AppxPackage is often broken or unavailable, so the standard wsl --install route fails. Use wsl --import with a rootfs tarball instead:

Now use a non-admin powershell:

mkdir $HOME\WSL
mkdir $HOME\WSL\Ubuntu

Then:

wsl --import Ubuntu $HOME\WSL\Ubuntu .\ubuntu.tar.gz --version 1

What you lose with WSL1: no Docker, no real Linux kernel, no systemd, weaker filesystem compatibility. Fine for CLI tooling, scripting, and build environments. If you need a real kernel, spin up a native Linux EC2 instance instead.