init

internal/security/csrf.go

@@ -0,0 +1,52 @@
+package security
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"net/http"
+)
+
+type CSRFFuncs struct {
+	// Read session for csrf value
+	GetCSRF func(r *http.Request) (token string, ok bool)
+	// Save ensures session has csrf value
+	EnsureCSRF func(w http.ResponseWriter, r *http.Request) (token string, err error)
+}
+
+func NewCSRFToken() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+func CSRFMiddleware(f CSRFFuncs) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			// Always ensure csrf exists for HTML GET requests
+			if r.Method == http.MethodGet || r.Method == http.MethodHead {
+				_, _ = f.EnsureCSRF(w, r)
+				next.ServeHTTP(w, r)
+				return
+			}
+			// Validate for unsafe methods
+			token, ok := f.GetCSRF(r)
+			if !ok || token == "" {
+				http.Error(w, "csrf missing", http.StatusForbidden)
+				return
+			}
+			// Prefer header (JS), fallback to form value
+			got := r.Header.Get("X-CSRF-Token")
+			if got == "" {
+				_ = r.ParseForm()
+				got = r.Form.Get("csrf")
+			}
+			if got == "" || got != token {
+				http.Error(w, "csrf mismatch", http.StatusForbidden)
+				return
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}