Missing Authentication in Chi

Missing authentication in Chi-based APIs creates multiple attack vectors that exploit the framework's design patterns. The most common manifestation occurs in Chi's route handler chain, where developers assume middleware will always be present but fail to enforce authentication at the handler level.

Consider a typical Chi router setup:

router := chi.NewRouter()
router.Use(middleware.Logger)
router.Use(middleware.Recoverer)
router.Use(authMiddleware) // Authentication middleware
router.Get("/api/users", listUsersHandler) // Protected endpoint
router.Post("/api/users", createUserHandler) // Protected endpoint

The vulnerability emerges when developers create sub-routers without explicitly inheriting middleware:

adminRouter := chi.NewRouter()
adminRouter.Get("/stats", adminStatsHandler) // No authMiddleware applied!
router.Mount("/admin", adminRouter) // Sub-router mounts without auth

This pattern allows unauthenticated access to /admin/stats because the sub-router doesn't automatically inherit parent middleware. Attackers can exploit this by discovering admin endpoints through directory traversal or brute force.

Another Chi-specific manifestation involves context-based authentication state. Developers often store authentication results in the request context but fail to validate it in every handler:

func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        if token == "" {
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return
        }
        ctx := context.WithValue(r.Context(), "user_id", token)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

func someHandler(w http.ResponseWriter, r *http.Request) {
    // BUG: No context validation
    userID := r.Context().Value("user_id")
    if userID == nil {
        http.Error(w, "unauthorized", http.StatusUnauthorized)
        return
    }
    // Process request...
}

The context-based approach fails when handlers are called directly or when middleware is bypassed through router mounting.

Chi's pattern matching also creates authentication gaps. Wildcard routes like /* or /api/* can inadvertently expose sensitive endpoints if not properly secured:

router.Get("/api/*", catchAllHandler) // May expose admin endpoints

Attackers exploit these gaps by guessing endpoint patterns or using tools that automatically discover API surface areas.

Detecting missing authentication in Chi applications requires both static analysis and runtime scanning. The most effective approach combines code review with automated security scanning.

Static analysis should focus on Chi's router configuration patterns. Look for these red flags in your codebase:

// Red flag: Sub-routers without inherited middleware
adminRouter := chi.NewRouter()
adminRouter.Get("/sensitive", sensitiveHandler)
router.Mount("/admin", adminRouter) // No auth middleware

// Red flag: Direct handler assignments without middleware
router.Get("/api/data", directHandler) // No auth check

// Red flag: Context values without validation
func handler(w http.ResponseWriter, r *http.Request) {
    if r.Context().Value("user_id") == nil {
        // Missing auth check!
    }
}

Runtime detection with middleBrick specifically identifies Chi authentication gaps by analyzing the actual HTTP request flow. The scanner tests endpoints without authentication headers and observes responses:

middleBrick Authentication Detection Workflow:

• Scans all discovered endpoints without authentication headers
• Analyzes HTTP status codes and response patterns
• Identifies endpoints that should be protected but respond to unauthenticated requests
• Cross-references discovered endpoints with OpenAPI specifications if available
• Tests for common authentication bypass patterns specific to Go/HTTP frameworks

The scanner's Chi-specific detection includes testing for:

// What middleBrick tests:
GET /admin/stats HTTP/1.1
Host: example.com
// Should return 401/403 but returns 200 - authentication missing!

GET /api/users HTTP/1.1
Host: example.com
// Should require auth but accessible anonymously

middleBrick also analyzes Chi's context-based authentication patterns by examining how authentication state is propagated through the request chain. The scanner looks for handlers that access context values without proper validation.

For comprehensive coverage, integrate middleBrick into your CI/CD pipeline using the GitHub Action:

name: API Security Scan
on: [push, pull_request]
jobs:
  security:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - name: Run middleBrick Scan
      run: |
        npx middlebrick scan https://your-api.com --output json
      continue-on-error: true
    - name: Fail on High Risk
      run: |
        # Parse middleBrick JSON output
        # Fail if any critical/high severity authentication issues found

Remediating missing authentication in Chi requires a defense-in-depth approach that combines proper middleware usage, context validation, and endpoint protection patterns.

1. Enforce Authentication at Router Level

The most reliable pattern is to create a protected router that guarantees authentication for all endpoints:

func NewProtectedRouter() *chi.Mux {
    router := chi.NewRouter()
    router.Use(authMiddleware)
    
    // All routes here are automatically protected
    router.Get("/api/users", listUsersHandler)
    router.Post("/api/users", createUserHandler)
    router.Get("/admin/stats", adminStatsHandler)
    
    return router
}

func main() {
    r := chi.NewRouter()
    r.Mount("/", NewProtectedRouter())
    http.ListenAndServe(":8080", r)
}

This pattern ensures no endpoint can be added without going through the authentication middleware.

2. Context Validation Wrapper

Create a handler wrapper that validates authentication context in every handler:

func RequireAuth(next http.HandlerFunc) http.HandlerFunc {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Validate authentication context
        authContext := r.Context().Value("auth_context")
        if authContext == nil {
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return
        }
        next.ServeHTTP(w, r)
    })
}

// Usage:
router.Get("/api/data", RequireAuth(dataHandler))

3. Sub-Router Authentication Pattern

When using sub-routers, always apply authentication explicitly:

func NewAdminRouter() http.Handler {
    router := chi.NewRouter()
    router.Use(authMiddleware) // CRITICAL: Apply auth to sub-router
    
    // All admin endpoints automatically protected
    router.Get("/stats", adminStatsHandler)
    router.Post("/config", updateConfigHandler)
    
    return router
}

func main() {
    r := chi.NewRouter()
    r.Mount("/admin", NewAdminRouter())
    http.ListenAndServe(":8080", r)
}

4. Authentication Failure Detection

Add logging and monitoring to detect authentication bypass attempts:

func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        if token == "" {
            log.Printf("auth attempt: missing token from %s", r.RemoteAddr)
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return
        }
        
        // Validate token...
        if !valid {
            log.Printf("auth attempt: invalid token from %s", r.RemoteAddr)
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return
        }
        
        next.ServeHTTP(w, r)
    })
}

5. Automated Testing

Implement automated tests that verify authentication requirements:

func TestAuthentication(t *testing.T) {
    ts := httptest.NewServer(NewProtectedRouter())
    defer ts.Close()
    
    // Test unauthenticated access should fail
    resp, err := http.Get(ts.URL + "/api/users")
    if err != nil {
        t.Fatal(err)
    }
    if resp.StatusCode != http.StatusUnauthorized {
        t.Errorf("expected 401, got %d", resp.StatusCode)
    }
    
    // Test authenticated access should succeed
    req, _ := http.NewRequest("GET", ts.URL + "/api/users", nil)
    req.Header.Set("Authorization", "valid-token")
    resp, _ = http.DefaultClient.Do(req)
    if resp.StatusCode != http.StatusOK {
        t.Errorf("expected 200, got %d", resp.StatusCode)
    }
}