When you call a cross-origin endpoint that requires cookies, session tokens, or any credentialed auth, include credentials: 'include' in the fetch options. Browsers default to credentials: 'same-origin', which drops cookies on cross-origin requests — the backend rejects the call with 401/403 and the response fails CORS preflight.
immunize-fetch-missing-credentials is a community-contributed Claude Code skill in the security-misc sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/fetch-missing-credentials/ and loads when your prompt matches the skill's trigger.
When to invoke it: Use when writing cross-origin fetch() calls that require cookies or session auth to ensure `credentials: 'include'` is set.
The immunize-fetch-missing-credentials Claude Code skill is built for security engineers, penetration testers, DevSecOps practitioners, and development teams hardening codebases and infrastructure. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 116,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).
mkdir -p ~/.claude/skills/fetch-missing-credentials curl -L https://claudskills.com/skills/fetch-missing-credentials/SKILL.md \ -o ~/.claude/skills/fetch-missing-credentials/SKILL.md
Or just download SKILL.md directly and drop it into ~/.claude/skills/fetch-missing-credentials/. Claude Code auto-discovers it on next session.
Skills live at ~/.claude/skills/fetch-missing-credentials/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\fetch-missing-credentials\SKILL.md on Windows. See the full install guide for step-by-step instructions.
Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →
The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.
For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.
SKILL.md from the source repository to ~/.claude/skills/fetch-missing-credentials/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. immunize-fetch-missing-credentials is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Security category. Learn more at /learn/what-is-a-claude-skill/.If you reference this skill in a blog post, paper, or documentation, you can cite it as:
@misc{fetch-missing-credentials-2026,
author = {ClaudSkills},
title = {immunize-fetch-missing-credentials [Claude Code skill]},
year = {2026},
publisher = {ClaudSkills},
url = {https://claudskills.com/skills/fetch-missing-credentials/}
}Browse all Security skills in the ClaudSkills registry, or explore these other picks from the same category:
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SKILL.md files, not affiliated with, endorsed by, or sponsored by Anthropic.