add support for HSTS response headers

config/config.go

@@ -64,6 +64,13 @@ type Proxy struct {
 	TLSHeaderValue        string
 	GZIPContentTypes      *regexp.Regexp
 	RequestID             string
+	STSHeader             STSHeader
+}
+
+type STSHeader struct {
+	MaxAge     int
+	Subdomains bool
+	Preload    bool
 }
 
 type Runtime struct {

config/load.go

@@ -129,6 +129,9 @@ func load(cmdline, environ, envprefix []string, props *properties.Properties) (c
 	f.StringVar(&cfg.Proxy.TLSHeader, "proxy.header.tls", defaultConfig.Proxy.TLSHeader, "header for TLS connections")
 	f.StringVar(&cfg.Proxy.TLSHeaderValue, "proxy.header.tls.value", defaultConfig.Proxy.TLSHeaderValue, "value for TLS connection header")
 	f.StringVar(&cfg.Proxy.RequestID, "proxy.header.requestid", defaultConfig.Proxy.RequestID, "header for reqest id")
+	f.IntVar(&cfg.Proxy.STSHeader.MaxAge, "proxy.header.sts.maxage", defaultConfig.Proxy.STSHeader.MaxAge, "enable and set the max-age value for HSTS")
+	f.BoolVar(&cfg.Proxy.STSHeader.Subdomains, "proxy.header.sts.subdomains", defaultConfig.Proxy.STSHeader.Subdomains, "direct HSTS to include subdomains")
+	f.BoolVar(&cfg.Proxy.STSHeader.Preload, "proxy.header.sts.preload", defaultConfig.Proxy.STSHeader.Preload, "direct HSTS to pass the preload directive")
 	f.StringVar(&gzipContentTypesValue, "proxy.gzip.contenttype", defaultValues.GZIPContentTypesValue, "regexp of content types to compress")
 	f.StringVar(&listenerValue, "proxy.addr", defaultValues.ListenerValue, "listener config")
 	f.StringVar(&certSourcesValue, "proxy.cs", defaultValues.CertSourcesValue, "certificate sources")

fabio.properties

@@ -398,6 +398,38 @@
 # proxy.header.requestid =
 
 
+# proxy.header.sts.maxage enables and configures the max-age of HSTS for TLS requests.
+# When set greater than zero this enables the Strict-Transport-Security header
+# and sets the max-age value in the header.
+#
+# The default is
+#
+# proxy.header.sts.maxage = 0
+
+
+# proxy.header.sts.subdomains instructs HSTS to include subdomains.
+# When set to true, the 'includeSubDomains' option will be added to
+# the Strict-Transport-Security header.
+#
+# The default is
+#
+# proxy.header.sts.subdomains = false
+
+
+# proxy.header.sts.preload instructs HSTS to include the preload directive.
+# When set to true, the 'preload' option will be added to the
+# Strict-Transport-Security header.
+#
+# Sending the preload directive from your site can have PERMANENT CONSEQUENCES
+# and prevent users from accessing your site and any of its subdomains if you
+# find you need to switch back to HTTP. Please read the details at
+# hstspreload.appspot.com/#removal before sending the header with "preload".
+#
+# The default is
+#
+# proxy.header.sts.preload = false
+
+
 # proxy.gzip.contenttype configures which responses should be compressed.
 #
 # By default, responses sent to the client are not compressed even if the

proxy/http_headers.go

@@ -10,6 +10,22 @@ import (
 	"github.com/fabiolb/fabio/config"
 )
 
+// addResponseHeaders adds/updates headers in the response
+func addResponseHeaders(w http.ResponseWriter, r *http.Request, cfg config.Proxy) error {
+	if r.TLS != nil && cfg.STSHeader.MaxAge > 0 {
+		sts := "max-age=" + i32toa(int32(cfg.STSHeader.MaxAge))
+		if cfg.STSHeader.Subdomains {
+			sts += "; includeSubdomains"
+		}
+		if cfg.STSHeader.Preload {
+			sts += "; preload"
+		}
+		w.Header().Set("Strict-Transport-Security", sts)
+	}
+
+	return nil
+}
+
 // addHeaders adds/updates headers in request
 //
 // * add/update `Forwarded` header
@@ -130,6 +146,29 @@ func uint16base16(n uint16) string {
 	return string(b)
 }
 
+// i32toa is a faster implentation of strconv.Itoa() without importing another library
+// https://stackoverflow.com/a/39444005
+func i32toa(n int32) string {
+	buf := [11]byte{}
+	pos := len(buf)
+	i := int64(n)
+	signed := i < 0
+	if signed {
+		i = -i
+	}
+	for {
+		pos--
+		buf[pos], i = '0'+byte(i%10), i/10
+		if i == 0 {
+			if signed {
+				pos--
+				buf[pos] = '-'
+			}
+			return string(buf[pos:])
+		}
+	}
+}
+
 // scheme derives the request scheme used on the initial
 // request first from headers and then from the connection
 // using the following heuristic:

proxy/http_headers_test.go

@@ -4,6 +4,7 @@ import (
 	"crypto/tls"
 	"fmt"
 	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/fabiolb/fabio/config"
@@ -386,6 +387,70 @@ func TestAddHeaders(t *testing.T) {
 	}
 }
 
+func TestAddResponseHeaders(t *testing.T) {
+	tests := []struct {
+		desc string
+		r    *http.Request
+		cfg  config.Proxy
+		hdrs http.Header
+		err  string
+	}{
+		{"set Strict-Transport-Security for TLS, if MaxAge greater than 0",
+			&http.Request{RemoteAddr: "1.2.3.4:5555", TLS: &tls.ConnectionState{}},
+			config.Proxy{STSHeader: config.STSHeader{MaxAge: 31536000}},
+			http.Header{
+				"Strict-Transport-Security": []string{"max-age=31536000"},
+			},
+			"",
+		},
+
+		{"set Strict-Transport-Security with options for TLS, if MaxAge greater than 0 with options",
+			&http.Request{RemoteAddr: "1.2.3.4:5555", TLS: &tls.ConnectionState{}},
+			config.Proxy{STSHeader: config.STSHeader{MaxAge: 31536000, Preload: true, Subdomains: true}},
+			http.Header{
+				"Strict-Transport-Security": []string{"max-age=31536000; includeSubdomains; preload"},
+			},
+			"",
+		},
+
+		{"skip Strict-Transport-Security for non-TLS, if MaxAge greater than 0",
+			&http.Request{RemoteAddr: "1.2.3.4:5555"},
+			config.Proxy{STSHeader: config.STSHeader{MaxAge: 31536000}},
+			http.Header{},
+			"",
+		},
+	}
+
+	for i, tt := range tests {
+		tt := tt // capture loop var
+
+		t.Run(tt.desc, func(t *testing.T) {
+			if tt.r.Header == nil {
+				tt.r.Header = http.Header{}
+			}
+
+			w := httptest.NewRecorder()
+			err := addResponseHeaders(w, tt.r, tt.cfg)
+
+			if err != nil {
+				if got, want := err.Error(), tt.err; got != want {
+					t.Fatalf("%d: %s\ngot  %q\nwant %q", i, tt.desc, got, want)
+				}
+				return
+			}
+
+			if tt.err != "" {
+				t.Fatalf("%d: got nil want %q", i, tt.err)
+				return
+			}
+
+			resp := w.Result()
+			got, want := resp.Header, tt.hdrs
+			verify.Values(t, "", got, want)
+		})
+	}
+}
+
 func TestLocalPort(t *testing.T) {
 	tests := []struct {
 		r    *http.Request

proxy/http_proxy.go

@@ -130,6 +130,11 @@ func (p *HTTPProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if err := addResponseHeaders(w, r, p.Config); err != nil {
+		http.Error(w, "cannot add response headers", http.StatusInternalServerError)
+		return
+	}
+
 	upgrade, accept := r.Header.Get("Upgrade"), r.Header.Get("Accept")
 
 	tr := p.Transport