add support for auth keys

Add a middleware that requires authorization for all POST, PUT, and
DELETE requests. This is done using the Authorization header and the
provided auth key is then checked against a file containing scrypted
auth keys. These keys are salted the constant string `linx-server`.

README.md

@@ -30,6 +30,7 @@ Command-line options
 - ```-xframeoptions "..." ``` -- X-Frame-Options header (default is "SAMEORIGIN")
 - ```-remoteuploads``` -- (optionally) enable remote uploads (/upload?url=https://...) 
 - ```-realip``` -- (optionally) let linx-server know you (nginx, etc) are providing the X-Real-IP and/or X-Forwarded-For headers.
+- ````-authfile``` -- (optionally) require authorization for upload/delete by providing a newline-separated file of scrypted auth keys
 - ```-fastcgi``` -- (optionally) serve through fastcgi 
 - ```-nologs``` -- (optionally) disable request logs in stdout
 

auth.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"bufio"
+	"encoding/base64"
+	"net/http"
+	"os"
+	"strings"
+
+	"golang.org/x/crypto/scrypt"
+)
+
+const (
+	authPrefix   = "Linx "
+	scryptSalt   = "linx-server"
+	scryptN      = 16384
+	scryptr      = 8
+	scryptp      = 1
+	scryptKeyLen = 32
+)
+
+type AuthOptions struct {
+	AuthFile      string
+	UnauthMethods []string
+}
+
+type uploadBasicAuth struct {
+	successHandler http.Handler
+	failureHandler http.Handler
+	o              AuthOptions
+}
+
+func checkAuth(authFile string, decodedAuth []byte) (result bool, err error) {
+	f, err := os.Open(authFile)
+	if err != nil {
+		return
+	}
+
+	checkKey, err := scrypt.Key([]byte(decodedAuth), []byte(scryptSalt), scryptN, scryptr, scryptp, scryptKeyLen)
+	if err != nil {
+		return
+	}
+
+	encodedKey := base64.StdEncoding.EncodeToString(checkKey)
+
+	scanner := bufio.NewScanner(bufio.NewReader(f))
+	for scanner.Scan() {
+		if encodedKey == scanner.Text() {
+			result = true
+			return
+		}
+	}
+
+	result = false
+	err = scanner.Err()
+	return
+}
+
+func (a uploadBasicAuth) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if sliceContains(a.o.UnauthMethods, r.Method) {
+		// allow unauthenticated methods
+		a.successHandler.ServeHTTP(w, r)
+		return
+	}
+
+	authHeader := r.Header.Get("Authorization")
+	if !strings.HasPrefix(authHeader, authPrefix) {
+		a.failureHandler.ServeHTTP(w, r)
+		return
+	}
+
+	decodedAuth, err := base64.StdEncoding.DecodeString(authHeader[len(authPrefix):])
+	if err != nil {
+		a.failureHandler.ServeHTTP(w, r)
+		return
+	}
+
+	result, err := checkAuth(a.o.AuthFile, decodedAuth)
+	if err != nil || !result {
+		a.failureHandler.ServeHTTP(w, r)
+		return
+	}
+
+	a.successHandler.ServeHTTP(w, r)
+}
+
+func UploadAuth(o AuthOptions) func(http.Handler) http.Handler {
+	fn := func(h http.Handler) http.Handler {
+		return uploadBasicAuth{
+			successHandler: h,
+			failureHandler: http.HandlerFunc(badAuthorizationHandler),
+			o:              o,
+		}
+	}
+	return fn
+}
+
+func badAuthorizationHandler(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusUnauthorized)
+	http.Error(w, http.StatusText(http.StatusUnauthorized), http.StatusUnauthorized)
+}
+
+func sliceContains(slice []string, s string) bool {
+	for _, v := range slice {
+		if s == v {
+			return true
+		}
+	}
+
+	return false
+}

server.go

@@ -35,6 +35,7 @@ var Config struct {
 	allowHotlink              bool
 	fastcgi                   bool
 	remoteUploads             bool
+	authFile                  string
 }
 
 var Templates = make(map[string]*pongo2.Template)
@@ -64,6 +65,13 @@ func setup() *web.Mux {
 		frame:  Config.xFrameOptions,
 	}))
 
+	if Config.authFile != "" {
+		mux.Use(UploadAuth(AuthOptions{
+			AuthFile:      Config.authFile,
+			UnauthMethods: []string{"GET", "HEAD", "OPTIONS", "TRACE"},
+		}))
+	}
+
 	// make directories if needed
 	err := os.MkdirAll(Config.filesDir, 0755)
 	if err != nil {
@@ -103,9 +111,15 @@ func setup() *web.Mux {
 	selifIndexRe := regexp.MustCompile(`^/selif/$`)
 	torrentRe := regexp.MustCompile(`^/(?P<name>[a-z0-9-\.]+)/torrent$`)
 
+	if Config.authFile == "" {
 		mux.Get("/", indexHandler)
 		mux.Get("/paste/", pasteHandler)
+	} else {
+		mux.Get("/", http.RedirectHandler("/API", 303))
+		mux.Get("/paste/", http.RedirectHandler("/API/", 303))
+	}
 	mux.Get("/paste", http.RedirectHandler("/paste/", 301))
+
 	mux.Get("/API/", apiDocHandler)
 	mux.Get("/API", http.RedirectHandler("/API/", 301))
 
@@ -159,6 +173,8 @@ func main() {
 		"serve through fastcgi")
 	flag.BoolVar(&Config.remoteUploads, "remoteuploads", false,
 		"enable remote uploads")
+	flag.StringVar(&Config.authFile, "authfile", "",
+		"path to a file containing newline-separated scrypted auth keys")
 	flag.StringVar(&Config.contentSecurityPolicy, "contentsecuritypolicy",
 		"default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'; referrer none;",
 		"value of default Content-Security-Policy header")

server_test.go

@@ -52,6 +52,26 @@ func TestIndex(t *testing.T) {
 	}
 }
 
+func TestIndexAuthKeys(t *testing.T) {
+	Config.authFile = "/dev/null"
+
+	mux := setup()
+	w := httptest.NewRecorder()
+
+	req, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != 303 {
+		t.Fatalf("Status code is not 301, but %d", w.Code)
+	}
+
+	Config.authFile = ""
+}
+
 func TestNotFound(t *testing.T) {
 	mux := setup()
 	w := httptest.NewRecorder()