Security

What it does

When your agent uses it

• Adding login flows
• Handling user input

Example prompts

• “/security”

Workflow steps

7 steps, taken from the first numbered list in SKILL.md.

1. 1VALIDATE AT BOUNDARIES — Never trust client input. All data through changesets
2. 2NEVER INTERPOLATE USER INPUT — Use Ecto's ^ operator, never string interpolation
3. 3NO String.to_atom WITH USER INPUT — Atom exhaustion DoS. Use to_existing_atom/1
4. 4AUTHORIZE EVERYWHERE — Check in contexts AND re-validate in LiveView events
5. 5ESCAPE BY DEFAULT — Never use raw/1 with untrusted content
6. 6SECRETS NEVER IN CODE — All secrets in runtime.exs from env vars
7. 7LIVEVIEW EVENT PARAMS ARE UNTRUSTED — Users can alter forms, hooks, and every phx-value-* in DevTools. Validate and authorize against…

What it can do on your machine

Read from SKILL.md and the folder at commit 9767a82. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are elixir).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Security loads about 1k tokens when it runs, and up to ~8.1k if it reads all its reference files. Until then it costs about 55 tokens; SKILL.md has 313 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~55

When it runs · the whole SKILL.md, loaded when a task matches

~1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~8.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from oliver-kriska/claude-elixir-phoenix at commit 9767a82, republished under its MIT licence (© oliver-kriska). 313 words, ~1,028 tokens.

name

security

description

Build and harden Phoenix auth and security — OAuth login, password hashing, sessions, RBAC, rate limiting, CSRF, XSS, SQL injection, secrets. Use when adding login flows or permissions, or handling user input.

def authenticate(email, password) do
  user = Repo.get_by(User, email: email)

  cond do
    user && Argon2.verify_pass(password, user.hashed_password) ->
      {:ok, user}
    user ->
      {:error, :invalid_credentials}
    true ->
      Argon2.no_user_verify()  # Timing attack prevention
      {:error, :invalid_credentials}
  end
end

# `id` is client input even when it came from phx-value-id.
# RE-AUTHORIZE IN EVERY EVENT HANDLER
def handle_event("delete", %{"id" => id}, socket) do
  post = Blog.get_post!(id)

  # Don't trust that mount authorized this action!
  with :ok <- Bodyguard.permit(Blog, :delete_post, socket.assigns.current_user, post) do
    Blog.delete_post(post)
    {:noreply, stream_delete(socket, :posts, post)}
  else
    _ -> {:noreply, put_flash(socket, :error, "Unauthorized")}
  end
end

# ✅ SAFE: Parameterized queries
from(u in User, where: u.name == ^user_input)

# ❌ VULNERABLE: String interpolation
from(u in User, where: fragment("name = '#{user_input}'"))

© oliver-kriska, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 7 other files (references) in targets/pi/skills/security of oliver-kriska/claude-elixir-phoenix.

• SKILL.md
• references/advanced-patterns.md
• references/authentication.md
• references/authorization.md
• references/input-validation.md
• references/oauth-linking.md
• references/rate-limiting.md
• references/security-headers.md

Open the folder on GitHubat commit 9767a82