Add support for stale directive for digest authenticator (#80)

* Improve digest authenticator to handle stale directive

digestAuth.go

@@ -35,7 +35,12 @@ func (d *DigestAuth) Authorize(c *http.Client, rq *http.Request, path string) er
 // Verify checks for authentication issues and may trigger a re-authentication
 func (d *DigestAuth) Verify(c *http.Client, rs *http.Response, path string) (redo bool, err error) {
 	if rs.StatusCode == 401 {
-		err = NewPathError("Authorize", path, rs.StatusCode)
+		if isStaled(rs) {
+			redo = true
+			err = ErrAuthChanged
+		} else {
+			err = NewPathError("Authorize", path, rs.StatusCode)
+		}
 	}
 	return
 }
@@ -162,3 +167,17 @@ func getDigestAuthorization(digestParts map[string]string) string {
 
 	return authorization
 }
+
+func isStaled(rs *http.Response) bool {
+	header := rs.Header.Get("Www-Authenticate")
+	if len(header) > 0 {
+		directives := strings.Split(header, ",")
+		for i := range directives {
+			name, value, _ := strings.Cut(strings.Trim(directives[i], " "), "=")
+			if strings.EqualFold(name, "stale") {
+				return strings.EqualFold(value, "true")
+			}
+		}
+	}
+	return false
+}

digestAuth_test.go

@@ -1,6 +1,7 @@
 package gowebdav
 
 import (
+	"errors"
 	"net/http"
 	"strings"
 	"testing"
@@ -33,3 +34,42 @@ func TestDigestAuthAuthorize(t *testing.T) {
 		t.Error("got wrong Authorization header: " + rq.Header.Get("Authorization"))
 	}
 }
+
+func TestDigestAuthVerify(t *testing.T) {
+	a := &DigestAuth{user: "user", pw: "password", digestParts: make(map[string]string, 0)}
+
+	// Nominal test: 200 OK response
+	rs := &http.Response{
+		Status:     "200 OK",
+		StatusCode: http.StatusOK,
+	}
+
+	redo, err := a.Verify(nil, rs, "/")
+
+	if err != nil {
+		t.Errorf("got error: %v, want nil", err)
+	}
+
+	if redo {
+		t.Errorf("got redo: %t, want false", redo)
+	}
+
+	// Digest expiration test: 401 Unauthorized response with stale directive in WWW-Authenticate header
+	rs = &http.Response{
+		Status:     "401 Unauthorized",
+		StatusCode: http.StatusUnauthorized,
+		Header: http.Header{
+			"Www-Authenticate": []string{"Digest realm=\"webdav\", nonce=\"YVvALpkdBgA=931bbf2b6fa9dda227361dba38a735f005fd9f97\", algorithm=MD5, qop=\"auth\", stale=true"},
+		},
+	}
+
+	redo, err = a.Verify(nil, rs, "/")
+
+	if !errors.Is(err, ErrAuthChanged) {
+		t.Errorf("got error: %v, want ErrAuthChanged", err)
+	}
+
+	if !redo {
+		t.Errorf("got redo: %t, want true", redo)
+	}
+}