package headers import ( "fmt" "net/http" "regexp" "strconv" "strings" "github.com/traefik/traefik/v3/pkg/config/dynamic" ) // Header is a middleware that helps setup a few basic security features. // A single headerOptions struct can be provided to configure which features should be enabled, // and the ability to override a few of the default values. type Header struct { next http.Handler hasCustomHeaders bool hasCorsHeaders bool headers *dynamic.Headers allowOriginRegexes []*regexp.Regexp } // NewHeader constructs a new header instance from supplied frontend header struct. func NewHeader(next http.Handler, cfg dynamic.Headers) (*Header, error) { hasCustomHeaders := cfg.HasCustomHeadersDefined() hasCorsHeaders := cfg.HasCorsHeadersDefined() regexes := make([]*regexp.Regexp, len(cfg.AccessControlAllowOriginListRegex)) for i, str := range cfg.AccessControlAllowOriginListRegex { reg, err := regexp.Compile(str) if err != nil { return nil, fmt.Errorf("error occurred during origin parsing: %w", err) } regexes[i] = reg } return &Header{ next: next, headers: &cfg, hasCustomHeaders: hasCustomHeaders, hasCorsHeaders: hasCorsHeaders, allowOriginRegexes: regexes, }, nil } func (s *Header) ServeHTTP(rw http.ResponseWriter, req *http.Request) { // Handle Cors headers and preflight if configured. if isPreflight := s.processCorsHeaders(rw, req); isPreflight { return } if s.hasCustomHeaders { s.modifyCustomRequestHeaders(req) } // If there is a next, call it. if s.next != nil { s.next.ServeHTTP(newResponseModifier(rw, req, s.PostRequestModifyResponseHeaders), req) } } // modifyCustomRequestHeaders sets or deletes custom request headers. func (s *Header) modifyCustomRequestHeaders(req *http.Request) { // Loop through Custom request headers for header, value := range s.headers.CustomRequestHeaders { switch { case value == "": req.Header.Del(header) case strings.EqualFold(header, "Host"): req.Host = value default: req.Header.Set(header, value) } } } // PostRequestModifyResponseHeaders set or delete response headers. // This method is called AFTER the response is generated from the backend // and can merge/override headers from the backend response. func (s *Header) PostRequestModifyResponseHeaders(res *http.Response) error { // Loop through Custom response headers for header, value := range s.headers.CustomResponseHeaders { if value == "" { res.Header.Del(header) } else { res.Header.Set(header, value) } } if res != nil && res.Request != nil { originHeader := res.Request.Header.Get("Origin") allowed, match := s.isOriginAllowed(originHeader) if allowed { res.Header.Set("Access-Control-Allow-Origin", match) } } if s.headers.AccessControlAllowCredentials { res.Header.Set("Access-Control-Allow-Credentials", "true") } if len(s.headers.AccessControlExposeHeaders) > 0 { exposeHeaders := strings.Join(s.headers.AccessControlExposeHeaders, ",") res.Header.Set("Access-Control-Expose-Headers", exposeHeaders) } if !s.headers.AddVaryHeader { return nil } varyHeader := res.Header.Get("Vary") if varyHeader == "Origin" { return nil } if varyHeader != "" { varyHeader += "," } varyHeader += "Origin" res.Header.Set("Vary", varyHeader) return nil } // processCorsHeaders processes the incoming request, // and returns if it is a preflight request. // If not a preflight, it handles the preRequestModifyCorsResponseHeaders. func (s *Header) processCorsHeaders(rw http.ResponseWriter, req *http.Request) bool { if !s.hasCorsHeaders { return false } reqAcMethod := req.Header.Get("Access-Control-Request-Method") originHeader := req.Header.Get("Origin") if reqAcMethod != "" && originHeader != "" && req.Method == http.MethodOptions { // If the request is an OPTIONS request with an Access-Control-Request-Method header, // and Origin headers, then it is a CORS preflight request, // and we need to build a custom response: https://www.w3.org/TR/cors/#preflight-request if s.headers.AccessControlAllowCredentials { rw.Header().Set("Access-Control-Allow-Credentials", "true") } allowHeaders := strings.Join(s.headers.AccessControlAllowHeaders, ",") if allowHeaders != "" { rw.Header().Set("Access-Control-Allow-Headers", allowHeaders) } allowMethods := strings.Join(s.headers.AccessControlAllowMethods, ",") if allowMethods != "" { rw.Header().Set("Access-Control-Allow-Methods", allowMethods) } allowed, match := s.isOriginAllowed(originHeader) if allowed { rw.Header().Set("Access-Control-Allow-Origin", match) } rw.Header().Set("Access-Control-Max-Age", strconv.Itoa(int(s.headers.AccessControlMaxAge))) return true } return false } func (s *Header) isOriginAllowed(origin string) (bool, string) { for _, item := range s.headers.AccessControlAllowOriginList { if item == "*" || item == origin { return true, item } } for _, regex := range s.allowOriginRegexes { if regex.MatchString(origin) { return true, origin } } return false, "" }