How to fix npm ERR! git clone git://github.com/user/private-repo.git failed npm ERR! fatal: Authentication failed in npm

Test Git access directly to rule out network or permission issues:

# For SSH access
ssh -T [email protected]

# For HTTPS access
git clone https://github.com/owner/private-repo.git

If SSH test fails with "Permission denied (publickey)", proceed to SSH setup.
If HTTPS test fails with authentication error, configure credentials.

Generate an SSH key and add it to your Git hosting service:

# Generate SSH key
ssh-keygen -t ed25519 -C "[email protected]"

# Start SSH agent and add key
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

# Display public key to copy to GitHub
cat ~/.ssh/id_ed25519.pub

Then:
1. Go to GitHub Settings > SSH and GPG keys
2. Click "New SSH key" and paste the public key
3. Test: ssh -T [email protected]

Update package.json to use SSH URLs:

{
  "dependencies": {
    "private-package": "git+ssh://[email protected]:owner/repo.git"
  }
}

If using HTTPS authentication, create a token:

1. Go to GitHub Settings > Developer settings > Personal access tokens
2. Generate new token with repo scope
3. Copy the token immediately

Configure in .npmrc:

//npm.pkg.github.com/:_authToken=YOUR_GITHUB_PAT

Or embed in package.json URL (less secure):

{
  "dependencies": {
    "private-package": "git+https://TOKEN:[email protected]/owner/repo.git"
  }
}

For GitHub Actions, GitLab CI, or Docker builds:

GitHub Actions:

- name: Install dependencies
  env:
    GIT_CREDENTIALS_FILE: /tmp/.git-credentials
  run: |
    echo "https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com" > $GIT_CREDENTIALS_FILE
    git config --global credential.helper "store --file=$GIT_CREDENTIALS_FILE"
    npm install

Docker (using build secrets):

RUN --mount=type=secret,id=github_token \
    git config --global credential.helper "store" && \
    npm install

Important: Never commit tokens to version control.

If using multiple Git hosts, configure SSH to use different keys:

Create or edit ~/.ssh/config:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/github_id_ed25519
  IdentitiesOnly yes

Host gitlab.com
  HostName gitlab.com
  User git
  IdentityFile ~/.ssh/gitlab_id_ed25519

Ensure SSH agent has keys loaded:

ssh-add ~/.ssh/github_id_ed25519
ssh-add ~/.ssh/gitlab_id_ed25519

If you have 2FA enabled and git cannot prompt interactively:

For HTTPS access, you MUST use a Personal Access Token (regular passwords no longer work):
- Create a PAT with repo scope
- Configure in .npmrc or environment variable
- Do NOT use your GitHub password

For SSH access, 2FA does not apply—SSH keys work normally even with 2FA enabled.