Broken Authentication in Chi with Basic Auth

Chi is a lightweight, asynchronous-first web framework for the Nim programming language. When Basic Authentication is used directly in a Chi application without additional protections, the framework’s typical flow of extracting headers and passing them downstream can unintentionally expose credentials or allow authentication bypass. Basic Auth encodes a username and password with Base64, which is reversible and not encrypted; if Chi routes or handlers do not enforce HTTPS and strict validation, an attacker can intercept or manipulate credentials in transit or via injection.

In a black-box scan using middleBrick, endpoints that rely solely on Basic Auth in Chi often reveal weaknesses such as missing transport-layer enforcement, overly permissive route matchers that accept credentials without verifying a secure context, and inconsistent handling of the Authorization header across middleware. For example, a Chi route that reads let auth = request.headers["Authorization"] and decodes the Base64 token without verifying the request’s TLS status can expose credentials to interception. Furthermore, if the application reuses the same handler for both authenticated and unauthenticated paths without clear separation, it may lead to Broken Authentication where access control is incorrectly applied, enabling BOLA/IDOR-like access to other users’ resources.

middleBrick’s checks for Authentication and BOLA/IDOR highlight these issues by probing unauthenticated surfaces and mapping findings to OWASP API Top 10 and PCI-DSS requirements. When scanning a Chi-based API, the tool detects whether the Authorization header is handled securely, whether credentials are validated against a backend identity store, and whether transport security is enforced. These checks are run in parallel with other security controls, providing a per-category breakdown that helps teams understand how Broken Authentication manifests specifically in Chi when Basic Auth is used without complementary safeguards like rate limiting and input validation.

Remediation focuses on ensuring that Basic Auth is only accepted over HTTPS, credentials are validated against a secure store, and the Authorization header is handled consistently across Chi routes and middleware. The following examples demonstrate secure patterns in Chi using the chimera and base64 standard packages, with explicit TLS checks and structured error handling.

import http/[responses, headers, cookies]
import base64
import tls

proc authenticate(req: Request): bool =
  let authHeader = req.headers.get("Authorization")
  if authHeader.isNil: return false
  if not req.isSecure: return false  # enforce HTTPS
  let parts = authHeader[].split(" ")
  if parts.len != 2 or parts[0] != "Basic": return false
  let decoded = try: base64.decode(parts[1]) except: ""
  if decoded == "": return false
  let creds = decoded.split(":")
  if creds.len != 2: return false
  let (username, password) = (creds[0], creds[1])
  # validate against a secure backend, e.g., a users table or LDAP
  return validateUser(username, password)

proc loginHandler(req: Request): Future[Response] {.async.} =
  if not authenticate(req):
    return newResponse(401, "WWW-Authenticate: Basic realm=\"api\"", "Unauthorized")
  # proceed with authenticated logic
  return newOkResponse("Authenticated")

# Mount with Chi ensuring TLS is terminated at the proxy or server level
let r = newRouter()
r.get("/secure", loginHandler)

This pattern enforces HTTPS by checking req.isSecure, validates the format of the Basic Auth header, decodes credentials safely, and separates validation logic to avoid hardcoding secrets. It also returns a proper 401 with a WWW-Authenticate header to prompt clients correctly. For production use, integrate this with a secure credential store and apply middleware-level checks to ensure all routes requiring authentication use the same helper, reducing the risk of inconsistent handling that leads to Broken Authentication.

middleBrick’s CLI can be used to verify these fixes by scanning the endpoint after changes: middlebrick scan <url>. The dashboard and Pro plan continuous monitoring allow teams to track security scores over time and ensure that remediation steps such as enforcing HTTPS and validating headers remain effective across deployments. The GitHub Action can fail builds if the Authentication score drops, while the MCP Server enables scanning directly from IDEs during development.