TIL: Debugging SSH Access to GitHub Enterprise

The Problem

Cloning a repository failed with "Repository not found" even though I could see it in my browser.

The Root Cause

My SSH key was linked to my personal GitHub account, but the repository belonged to my Enterprise account.

How I Diagnosed It

# Test which account SSH authenticates as
# ssh -T git@github.com
# Output: "Hi personal-username!" ← Wrong account!

# See which key SSH is using (verbose mode)
# ssh -vT git@github.com
# Look for: "Server accepts key: /path/to/keyfile"

The Fix

1. Add SSH key to Enterprise account — Settings → SSH and GPG keys → New SSH key
2. Authorize for SSO — Click "Configure SSO" → Authorize for your organization
3. Update ~/.ssh/config to use the correct key
4. Clear cached keys and verify

# SSH config should look like:
# Host github.com
#   HostName github.com
#   User git
#   IdentityFile ~/.ssh/id_ed25519

# Clear cached keys
# ssh-add -D

# Verify correct account
# ssh -T git@github.com
# Output: "Hi enterprise-username!" ← Correct!

Key Commands Reference

# View SSH files
# ls -ltr ~/.ssh/
# cat ~/.ssh/config

# Generate new key
# ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -C "email" -N ""

# Show key fingerprint
# ssh-keygen -lf ~/.ssh/id_ed25519.pub

# Copy public key to clipboard (Mac)
# pbcopy < ~/.ssh/id_ed25519.pub

# Test SSH with specific key
# ssh -i ~/.ssh/id_ed25519 -T git@github.com

Key Insight

GitHub shows "Repository not found" for both non-existent repos AND repos you don't have access to — for security reasons. So when debugging, always verify which account your SSH key authenticates as!