JWT认证中Refresh Token的使用及实现相关问题咨询

Hey there! Let's walk through each of your questions about refresh tokens—they're key for building a smooth "remember me" feature, so these are great things to clarify.

1. Does a Refresh Token have to be a JWT, or can it be a hashed string? #

Nope, refresh tokens don't have to be JWTs—both options are valid, and which you pick depends on your use case:

• Hashed random strings: This is a super common approach. You generate a long, cryptographically random string (like a 64-character alphanumeric), store its hash in your database, and send the plaintext string to the client. When the client sends it back, you hash the incoming string and compare it to the hash in your DB. This is simple and secure, especially if you need to revoke tokens easily.
• JWTs: You can also use a signed JWT as a refresh token. The JWT can embed metadata like user ID, token expiration, or even a unique token ID (jti). The upside is you can validate the token's signature without hitting the database every time, but you lose easy revocation unless you track jtis in your DB too.

2. What are the advantages of using JWT for Refresh Tokens? #

If you opt for JWT refresh tokens, here's what you gain:

• Reduced database calls: Since JWTs are self-contained and signed, you can verify their validity (signature, expiration) without querying your DB for every refresh request. This can help with performance in high-traffic apps.
• Embedded metadata: You can include useful info directly in the token (like user ID, token version, or allowed scopes) instead of fetching that data from the DB each time.
• Stateless validation (mostly): If you don't need to support token revocation, you can avoid storing refresh tokens in your DB entirely—just rely on the JWT's signature and expiration to validate it. That said, most production apps still track refresh tokens to handle revocation, so this benefit is often limited.

3. Do Refresh Tokens need an expiration time? #

Absolutely—never use an infinite-lived refresh token, even for "remember me" features. Here's why:

• Security: If a refresh token is stolen, an attacker can keep using it indefinitely to get new access tokens unless you have a way to revoke it. Setting an expiration (like 30 days for your use case) limits the window of risk.
• User control: It gives users a natural "reset" point—if they haven't used the app in a month, they'll need to log in again, which is a good security practice.
• Compliance: Many security standards (like OAuth 2.0) recommend or require refresh tokens to have expiration times to minimize exposure.

4. Do I need to send the Refresh Token to the client? #

Yes, you do need to send it to the client—how else will they use it to request new access tokens when the old one expires? But you have to handle storage carefully to keep it secure:

• Web apps: Store the refresh token in an HttpOnly, Secure, and SameSite cookie. This prevents XSS attacks from stealing the token, and Secure ensures it's only sent over HTTPS.
• Mobile apps: Store the token in a secure device storage (like iOS Keychain or Android Keystore) instead of plaintext SharedPreferences or local storage.
• Database best practice: If you're using a random string refresh token, always store its hash in your DB (not the plaintext). For JWT refresh tokens, you can store the jti (unique token ID) so you can revoke it if needed (e.g., when the user logs out). When the client sends the JWT back, you check if the jti is still valid in your DB alongside verifying the JWT signature.

内容的提问来源于stack exchange，提问作者Vahid Najafi