Update Certbot dependency to Lexicon to 3.x (#6593)

This PR updates Lexicon dependency to the latest version available, 3.0.6, for every lexicon-based DNS plugins. It updates also the provider construction to use the new ConfigResolverobject, and to remove the legacy configuration process.

certbot/plugins/dns_common_lexicon.py

@@ -1,12 +1,22 @@
 """Common code for DNS Authenticator Plugins built on Lexicon."""
-
 import logging
 
 from requests.exceptions import HTTPError, RequestException
 
+from acme.magic_typing import Union, Dict, Any  # pylint: disable=unused-import,no-name-in-module
 from certbot import errors
 from certbot.plugins import dns_common
 
+# Lexicon is not declared as a dependency in Certbot itself,
+# but in the Certbot plugins backed by Lexicon.
+# So we catch import error here to allow this module to be
+# always importable, even if it does not make sense to use it
+# if Lexicon is not available, obviously.
+try:
+    from lexicon.config import ConfigResolver
+except ImportError:
+    ConfigResolver = None  # type: ignore
+
 logger = logging.getLogger(__name__)
 
 
@@ -100,3 +110,28 @@ class LexiconClient(object):
         if not str(e).startswith('No domain found'):
             return errors.PluginError('Unexpected error determining zone identifier for {0}: {1}'
                                       .format(domain_name, e))
+
+
+def build_lexicon_config(lexicon_provider_name, lexicon_options, provider_options):
+    # type: (str, Dict, Dict) -> Union[ConfigResolver, Dict]
+    """
+    Convenient function to build a Lexicon 2.x/3.x config object.
+    :param str lexicon_provider_name: the name of the lexicon provider to use
+    :param dict lexicon_options: options specific to lexicon
+    :param dict provider_options: options specific to provider
+    :return: configuration to apply to the provider
+    :rtype: ConfigurationResolver or dict
+    """
+    config = {'provider_name': lexicon_provider_name}  # type: Dict[str, Any]
+    config.update(lexicon_options)
+    if not ConfigResolver:
+        # Lexicon 2.x
+        config.update(provider_options)
+    else:
+        # Lexicon 3.x
+        provider_config = {}
+        provider_config.update(provider_options)
+        config[lexicon_provider_name] = provider_config
+        config = ConfigResolver().with_dict(config).with_env()
+
+    return config