Man In The Middle in Chi with Basic Auth

In Chi, Basic Authentication transmits credentials in an Authorization header that is base64-encoded but not encrypted. A Man In The Middle (MitM) can intercept this header in transit and decode it to recover the username and password. This risk is elevated when requests do not use strong transport-layer protections, allowing an attacker on the same network to observe and manipulate unauthenticated API interactions.

Because middleBrick scans the unauthenticated attack surface, it can detect whether an API relies on Basic Auth without enforcing transport security and whether any endpoints expose credentials in cleartext over HTTP. The scanner also evaluates whether the API uses hostnames and paths that could be targeted for session interception. Even when the API uses Basic Auth, without HTTPS and additional protections, credentials can be stolen and reused.

Chi frameworks often rely on standard HTTP clients, and developers may inadvertently allow insecure HTTP calls or fail to redirect HTTP to HTTPS. middleBrick identifies these misconfigurations by checking for the presence of TLS and validating that sensitive endpoints require secure transport. The tool also examines whether the API leaks credentials via logs, error messages, or improper caching, which can compound the impact of an intercepted Basic Auth header.

Another dimension involves the handling of the Authorization header itself. If the header is included in requests that are logged, proxied, or cached, the risk of accidental exposure increases. middleBrick reviews runtime behavior and OpenAPI specifications to confirm that security-related headers are consistently enforced and that $ref-resolved definitions do not omit critical security requirements.

Finally, the scanner checks for SSRF and related network exposures that could facilitate an internal MitM scenario, where an attacker positioned within the infrastructure can observe traffic between services. By correlating spec definitions with runtime findings, middleBrick highlights whether Basic Auth is used in contexts where stronger mechanisms, such as token-based authentication, would reduce the attack surface.

Remediation focuses on eliminating cleartext transmission of credentials and ensuring that the Authorization header is never exposed in logs or error responses. The primary fix is to enforce HTTPS for all endpoints that use Basic Auth and to avoid sending credentials in query parameters or headers that are not protected by TLS.

Chi HTTP client with HTTPS and Basic Auth

Use a configured HTTP client that enforces secure transport. The following example demonstrates a secure Chi endpoint definition that requires TLS and sends Basic Auth only over HTTPS:

(define (secure-handler request)
  (let* ((auth-header (request-header request "authorization"))
         (valid (and auth-header
                     (string-prefix? "Basic " auth-header)
                     (verify-credentials (base64-decode (substring auth-header 6))))))
    (if valid
        (response/json '((status "ok"))
                        #:status 200)
        (response/json '((error "unauthorized"))
                        #:status 401))))

(define (start-server)
  (serve #:port 443
         #:tls (tls-server-cert "server.crt")
         #:tls-key (tls-server-key "server.key")
         #:dispatch (dispatch '((GET ("/api/resource" . secure-handler))))))

Enforcing HTTPS redirects in Chi

Ensure that HTTP traffic is redirected to HTTPS before any authentication processing occurs:

(define (redirect-to-https request)
  (response/redirect (string-append "https://" (request-header request "host") (request-uri request))
                     #:status 301))

(define (insecure-entry-point)
  (serve #:port 80
         #:dispatch '((GET ("/" . redirect-to-https)))))

Avoiding credential leakage in logs and errors

Ensure that the Authorization header is stripped from logs and that error messages do not echo header values:

(define (sanitized-logging-middleware handler)
  (lambda (request)
    (let ((filtered-headers (filter (lambda (h)
                                     (not (equal? (car h) "authorization")))
                                   (request-headers request))))
      (handler (make-request (request-uri request)
                             (request-method request)
                             #:headers filtered-headers))))

Prefer token-based authentication where feasible

While the above fixes reduce risk, Basic Auth over HTTPS still transmits credentials with each request. Where possible, migrate to token-based flows and use the middleBrick CLI to validate that tokens are handled securely:

$ middlebrick scan https://api.example.com --output json

Use the middleBrick Web Dashboard to track security scores over time and the GitHub Action to fail builds if risk scores degrade. The Pro plan supports continuous monitoring and CI/CD integration for ongoing assurance.