Fix Broken User Authentication in LoopBack

LoopBack 4's modularity often leads developers to implement 'lean' authentication that bypasses critical security controls. Broken authentication typically manifests as weak credential storage, susceptibility to brute-force, or improper session management. To harden a LoopBack application, we must move away from manual credential checks and integrate robust hashing with the @loopback/authentication component.

The Vulnerable Pattern

async verifyCredentials(credentials: Credentials): Promise {
  const foundUser = await this.userRepository.findOne({
    where: {email: credentials.email},
  });
  if (!foundUser || foundUser.password !== credentials.password) {
    // VULNERABILITY: Plain-text comparison and potential timing attack
    throw new HttpErrors.Unauthorized('Invalid email or password');
  }
  return foundUser;
}

The Secure Implementation

The vulnerable code performs a direct string comparison on passwords, which is a catastrophic failure allowing anyone with database access to hijack accounts. It also lacks protection against timing attacks. The secure implementation utilizes 'bcryptjs' to handle salted password hashes. By using 'await compare()', we ensure that the computation time is relatively constant, mitigating side-channel attacks. Furthermore, the error messages are kept generic to prevent 'Username Enumeration'—an attacker shouldn't know if the email exists or just the password was wrong. For full production hardening, this should be coupled with the @loopback/authentication 'AuthenticationComponent' and a rate-limiting middleware to stop automated brute-force attempts.

import {compare} from 'bcryptjs';
async verifyCredentials(credentials: Credentials): Promise {
const foundUser = await this.userRepository.findOne({
where: {email: credentials.email},
});
if (!foundUser) {
throw new HttpErrors.Unauthorized(‘Invalid email or password’);
}
// FIX: Use bcrypt for constant-time comparison and salted hash validation
const passwordMatched = await compare(
credentials.password,
foundUser.password,
);
if (!passwordMatched) {
throw new HttpErrors.Unauthorized(‘Invalid email or password’);
}
return foundUser;
}