apache: fix crash when authenticating empty vhosts (#8941)

Fixes #8940.

certbot-apache/certbot_apache/_internal/parser.py

@@ -440,7 +440,11 @@ class ApacheParser:
         :type args: list or str
         """
         first_dir = aug_conf_path + "/directive[1]"
-        self.aug.insert(first_dir, "directive", True)
+        if self.aug.get(first_dir):
+            self.aug.insert(first_dir, "directive", True)
+        else:
+            self.aug.set(first_dir, "directive")
+
         self.aug.set(first_dir, dirname)
         if isinstance(args, list):
             for i, value in enumerate(args, 1):

certbot-apache/tests/parser_test.py

@@ -105,6 +105,11 @@ class BasicParserTest(util.ParserTest):
         for i, match in enumerate(matches):
             self.assertEqual(self.parser.aug.get(match), str(i + 1))
 
+        for name in ("empty.conf", "no-directives.conf"):
+            conf = "/files" + os.path.join(self.parser.root, "sites-available", name)
+            self.parser.add_dir_beginning(conf, "AddDirectiveBeginning", "testBegin")
+            self.assertTrue(self.parser.find_dir("AddDirectiveBeginning", "testBegin", conf))
+
     def test_empty_arg(self):
         self.assertEqual(None,
                           self.parser.get_arg("/files/whatever/nonexistent"))

certbot-apache/tests/testdata/debian_apache_2_4/multiple_vhosts/apache2/sites-available/no-directives.conf

@@ -0,0 +1,5 @@
+<VirtualHost *:80>
+  <Location />
+        Require all denied
+  </Location>
+</VirtualHost>

certbot/CHANGELOG.md

@@ -18,7 +18,8 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
 
 ### Fixed
 
-*
+* The Apache authenticator no longer crashes with "Unable to insert label"
+  when encountering a completely empty vhost. This issue affected Certbot 1.17.0.
 
 More details about these changes can be found on our GitHub repo.