fastapi-security

A set of security guidelines for FastAPI, a Python framework for web APIs. It covers bearer-token login, identifying the current user, protecting routes, securely storing passwords, and issuing tokens.

In plain words
What is it for?
Implementing or reviewing OAuth2-style authentication, password hashing, protected route groups, current-user checks, and login token endpoints.
Why use it?
It helps prevent common authentication mistakes, such as storing passwords in plain text or leaving API routes unprotected.

Skill for Claude CodeCodex

Part of the fastapi-best-practices plugin — 3 skills shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/dkmqflx/fastapi-best-practices-plugin/fastapi-security
Any agent
npx skills add dkmqflx/fastapi-best-practices-plugin --skill fastapi-security
Clone the repo
git clone --depth 1 https://github.com/dkmqflx/fastapi-best-practices-plugin

Made for: Claude Code, Codex.

Or install fastapi-best-practices, the plugin that ships this one along with the rest of its 3 skills.

Per session 65 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 501 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00065 $0.00501
Opus 5 $0.00032 $0.00251
Sonnet 5 $0.00013 $0.00100
Haiku 4.5 $0.00006 $0.00050

Measured 2d ago against content hash 5e14715b9804, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fastapi-security scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/fastapi-best-practices/skills/fastapi-security/SKILL.md · 54 lines

What it actually says

FastAPI Security & Authentication

Best practices for securing FastAPI applications, following the official security docs (https://fastapi.tiangolo.com/tutorial/security/). Covers extracting and validating Bearer tokens, resolving the current user as a dependency, protecting route groups, hashing passwords, and building the token-issuing endpoint. Each rule pairs an antipattern with the official FastAPI pattern.

When to Apply

Reference these guidelines when:

  • Extracting or validating a Bearer token from the Authorization header
  • Resolving the current authenticated user in a dependency
  • Protecting a group of routes at the APIRouter level
  • Hashing and verifying passwords
  • Building the /token (or equivalent) login endpoint

Rules

  • oauth2-bearer (CRITICAL) — extract Bearer tokens with OAuth2PasswordBearer + Annotated
  • get-current-user (CRITICAL) — resolve the current user in a get_current_user dependency
  • router-auth (HIGH) — protect route groups via APIRouter(dependencies=[...])
  • password-hashing (CRITICAL) — hash passwords (pwdlib/passlib); never store plaintext
  • token-endpoint (HIGH) — build the token route with OAuth2PasswordRequestForm

How to Use

Read the individual rule file for the detailed explanation and before/after example:

rules/oauth2-bearer.md
rules/get-current-user.md
rules/router-auth.md
rules/password-hashing.md
rules/token-endpoint.md

Each rule file contains:

  • A short explanation of why it matters, tied to the official docs
  • An Incorrect example (the antipattern)
  • A Correct example (the official pattern)
  • A link to the relevant page on https://fastapi.tiangolo.com/

All examples follow the official FastAPI documentation and avoid deprecated APIs.

Files

What ships with it

5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 54 lines · 65 tokens per session scan A 5e14715b9804

Subscribe to this mod's changes

fastapi-security is a skill published in the GitHub repository dkmqflx/fastapi-best-practices-plugin (1 stars, last pushed 2mo ago), licensed MIT. It adds 65 tokens to every session and 501 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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