Token Leakage in Fiber with Api Keys

Token leakage in Go Fiber applications often occurs when API keys are handled without adequate safeguards. Because API keys are frequently passed in HTTP headers, query parameters, or cookies, they can be inadvertently exposed through logs, error messages, or misconfigured middleware. A common pattern in Fiber is reading keys from request headers and using them for authorization or routing decisions. If the application echoes headers in responses or logs them verbatim, an API key may be exposed to attackers who can inspect logs or intercept responses.

For example, consider a Fiber route that forwards requests to a downstream service using an API key taken directly from an incoming header. If the server includes that key in URLs or logs, an attacker with access to logs or network traces can harvest the key. Additionally, if the application returns detailed errors that include header values, a remote attacker can extract API keys via error responses. MiddleBrick’s authentication checks flag scenarios where API keys appear in responses or are transmitted without transport protections, helping to identify token leakage risks specific to API key usage patterns.

Another leakage vector arises from improper handling of API keys in middleware that caches or traces requests. If keys are included in cache keys or request identifiers stored in logs, they persist beyond the immediate request lifecycle. In distributed setups, keys may propagate unintentionally through headers forwarded to other services. MiddleBrick’s Data Exposure and Unsafe Consumption checks examine whether API keys are present in responses or logs, and whether encryption in transit is properly enforced across all endpoints that accept keys. These checks complement the broader authentication and encryption tests to highlight how token leakage can occur specifically through API key handling in Fiber services.

SSRF and improper external request configurations can also exacerbate token leakage. If a Fiber application uses an API key when making outbound requests and those requests are coerced to internal endpoints via SSRF, an attacker can trick the service into sending keys to internal listeners or metadata services. MiddleBrick’s SSRF checks validate that external request configurations do not inadvertently expose API keys to unauthorized internal endpoints. By correlating API key usage patterns with input validation and SSRF findings, the scanner provides a clearer view of how token leakage can emerge from seemingly unrelated configuration issues.

Finally, the absence of strict transport enforcement and weak validation of request origins can lead to token leakage via cross-origin or insecure requests. Without proper validation, an API key sent in a header may be reflected in responses to cross-origin callers, exposing the key to scripts controlled by attackers. MiddleBrick’s CORS-related findings and encryption checks help identify missing transport protections and unsafe reflection practices that contribute to token leakage in API key-driven Fiber applications.

To remediate token leakage when using API keys in Fiber, apply strict handling and transmission controls. First, avoid echoing API keys in responses or logs. Instead of logging raw headers, sanitize or omit sensitive values. Below is a Fiber handler that reads an API key from an Authorization header, validates it against a secure store, and ensures it is never included in logs or responses.

const jwt = require('jsonwebtoken');
const express = require('express');
const app = express();

const API_KEYS = new Set(['abc123', 'def456']); // in practice, use a secure store

app.use((req, res, next) => {
  const auth = req.headers['authorization'];
  if (auth && auth.startsWith('ApiKey ')) {
    const key = auth.slice(7);
    if (!API_KEYS.has(key)) {
      return res.status(401).send('Invalid API key');
    }
    // Do not log the key
    req.apiKey = key; // forward without exposing in logs
  }
  next();
});

app.get('/resource', (req, res) => {
  // Use the validated key for downstream calls without echoing it
  res.json({ data: 'secure resource' });
});

app.listen(3000, () => console.log('Server running on port 3000'));

Second, enforce HTTPS for all endpoints that accept or transmit API keys. Configure your server to reject cleartext HTTP and use strong cipher suites. MiddleBrick’s Encryption checks verify that endpoints requiring API keys mandate transport layer security, reducing the risk of interception.

const tls = require('tls');
const fs = require('fs');
const app = express();

const options = {
  key: fs.readFileSync('server.key'),
  cert: fs.readFileSync('server.cert'),
  minVersion: 'TLSv1.2',
  ciphers: 'TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256'
};

tls.createServer(options, app).listen(8443, () => {
  console.log('Secure server running on port 8443');
});

Third, avoid using API keys in URLs or query parameters, as they can leak via referrers, logs, or browser history. Prefer headers and ensure that any outgoing requests strip keys from URLs. MiddleBrick’s Input Validation findings can highlight parameters that may inadvertently carry sensitive tokens.

Fourth, implement strict access controls and rotate keys regularly. Use environment variables to inject keys at runtime rather than hardcoding them. Combine these practices with MiddleBrick’s continuous monitoring and CI/CD integrations (GitHub Action or MCP Server) to detect regressions early and enforce security gates before deployment.