106 lines
2.7 KiB
Go
106 lines
2.7 KiB
Go
package middleware
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import (
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"net/http"
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"strings"
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)
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// CSRFProtect returns middleware that validates the Origin header on
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// state-changing methods (POST, PUT, PATCH, DELETE).
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//
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// An origin is trusted if:
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// 1. It's in the explicit additionalOrigins list, OR
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// 2. Its hostname matches the configured host, OR
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// 3. Its hostname matches the request's own Host header (same-origin check)
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func CSRFProtect(host, port string, additionalOrigins []string) func(http.Handler) http.Handler {
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originSet := make(map[string]struct{})
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for _, o := range additionalOrigins {
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o = strings.TrimSpace(o)
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if o != "" {
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originSet[o] = struct{}{}
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}
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}
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hostname := host
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if idx := strings.LastIndex(hostname, ":"); idx > 0 {
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hostname = hostname[:idx]
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}
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return func(next http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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switch r.Method {
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case "POST", "PUT", "PATCH", "DELETE":
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origin := r.Header.Get("Origin")
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if origin == "" {
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referer := r.Header.Get("Referer")
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if referer != "" {
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for o := range originSet {
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if strings.HasPrefix(referer, o) {
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origin = o
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break
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}
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}
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}
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}
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if origin != "" {
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// Extract request host for same-origin check
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reqHost := r.Host
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if idx := strings.LastIndex(reqHost, ":"); idx > 0 {
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reqHost = reqHost[:idx]
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}
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if !isOriginTrusted(origin, hostname, port, reqHost, originSet) {
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http.Error(w, `{"error":"forbidden origin"}`, http.StatusForbidden)
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return
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}
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}
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}
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next.ServeHTTP(w, r)
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})
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}
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}
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func isOriginTrusted(origin, host, port, reqHost string, originSet map[string]struct{}) bool {
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if _, ok := originSet[origin]; ok {
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return true
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}
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withoutScheme := origin
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if idx := strings.Index(withoutScheme, "://"); idx >= 0 {
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withoutScheme = withoutScheme[idx+3:]
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}
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if idx := strings.Index(withoutScheme, "/"); idx >= 0 {
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withoutScheme = withoutScheme[:idx]
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}
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originHost := withoutScheme
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originPort := ""
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if idx := strings.LastIndex(originHost, ":"); idx >= 0 {
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originPort = originHost[idx+1:]
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originHost = originHost[:idx]
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}
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originHost = strings.TrimPrefix(originHost, "[")
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originHost = strings.TrimSuffix(originHost, "]")
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// Match configured host
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if host != "" && originHost == host {
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return true
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}
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// Match request's own Host header (same-origin)
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if reqHost != "" && originHost == reqHost {
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return true
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}
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// Localhost variants
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if originHost == "localhost" || originHost == "127.0.0.1" || originHost == "::1" {
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if port == "" || originPort == "" || originPort == port {
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return true
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}
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}
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return false
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}
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