TL;DR
Access tokens are sensitive credentials. Store them securely using these best practices: encrypt at rest, use short expiry times, rotate tokens regularly, and avoid storing them in easily accessible locations like client-side code or plain text files.
1. Understand the Risks
Access tokens grant applications permission to act on a user’s behalf. If compromised, attackers can:
- Impersonate users
- Access sensitive data
- Perform unauthorized actions
2. Encryption at Rest
Never store access tokens in plain text. Always encrypt them before saving them to a database, file system, or other storage medium.
- Database: Use database-level encryption (e.g., Transparent Data Encryption) or application-level encryption using a strong library.
- Filesystem: Encrypt the entire filesystem or encrypt individual token files before storing them.
Example (Python with Fernet):
from cryptography.fernet import Fernet
key = Fernet.generate_key()
f = Fernet(key)
token = b"your_sensitive_token"
enrypted_token = f.encrypt(token)
decrypted_token = f.decrypt(enrypted_token)3. Short Expiry Times
Reduce the window of opportunity for attackers by using short expiry times for access tokens.
- Consider token lifetime: Balance security with user experience. Shorter lifetimes mean more frequent re-authentication.
- Refresh Tokens: Use refresh tokens to obtain new access tokens without requiring the user to re-enter their credentials every time. Store refresh tokens even more securely than access tokens (see section 6).
4. Token Rotation
Regularly rotate access tokens, even if they haven’t expired.
- Automatic rotation: Implement a mechanism to automatically replace existing tokens with new ones at regular intervals.
- Revocation: Provide a way to revoke tokens immediately in case of compromise or user logout.
5. Secure Storage Locations
Avoid storing access tokens in insecure locations.
- Never in client-side code (JavaScript, etc.): Client-side code is easily accessible to attackers.
- Don’t store in plain text files: These are vulnerable to accidental exposure and unauthorized access.
- Use a dedicated secrets management system: Tools like HashiCorp Vault, AWS Secrets Manager, or Azure Key Vault provide secure storage and access control for sensitive credentials.
6. Refresh Token Security
Refresh tokens are even more critical than access tokens because they can be used to generate new access tokens indefinitely.
- Stronger Encryption: Use a different, stronger encryption key for refresh tokens compared to access tokens.
- Limited Scope: Restrict the scope of refresh tokens to only allow them to request new access tokens.
- IP Binding: Consider binding refresh tokens to the IP address from which they were issued (with appropriate caveats regarding dynamic IPs).
7. Access Control
Restrict access to token storage.
- Principle of Least Privilege: Grant only the necessary permissions to applications and users who need access to tokens.
- Auditing: Log all access to token storage for monitoring and security analysis.
8. Regular Security Audits
Periodically review your token storage implementation for vulnerabilities.
- Penetration testing: Conduct regular penetration tests to identify potential weaknesses.
- Code reviews: Have your code reviewed by security experts.