Extract authentication options handling into a separate function.

auth.py

Index: auth.py
diff --git a/auth.py b/auth.py
new file mode 100644
index 0000000000000000000000000000000000000000..97520deca3cdf4f47300fa694194a7ae2dc2b031
--- /dev/null
+++ b/auth.py
@@ -0,0 +1,99 @@
+# Copyright (c) 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Authentication related functions."""
+
+import collections
+import optparse
+
+
+# Authentication configuration extracted from command line options.
+# See doc string for 'make_auth_config' for meaning of fields.
+AuthConfig = collections.namedtuple('AuthConfig', [
+    'use_oauth2', # deprecated, will be always True
+    'save_cookies', # deprecated, will be removed
+    'use_local_webserver',
+    'webserver_port',
+])
+
+
+def make_auth_config(
+    use_oauth2=None,
+    save_cookies=None,
+    use_local_webserver=None,
+    webserver_port=None):
+  """Returns new instance of AuthConfig.
+
+  If some config option is None, it will be set to a reasonable default value.
+  This function also acts as an authoritative place for default values of
+  corresponding command line options.
+  """
+  default = lambda val, d: val if val is not None else d
+  return AuthConfig(
+      default(use_oauth2, False),
+      default(save_cookies, True),
+      default(use_local_webserver, True),
+      default(webserver_port, 8090))
+
+
+def add_auth_options(parser):
+  """Appends OAuth related options to OptionParser."""
+  default_config = make_auth_config()
+  parser.auth_group = optparse.OptionGroup(parser, 'Auth options')
+  parser.auth_group.add_option(
+      '--oauth2',
+      action='store_true',
+      dest='use_oauth2',
+      default=default_config.use_oauth2,
+      help='Use OAuth 2.0 instead of a password.')
+  parser.auth_group.add_option(
+      '--no-oauth2',
+      action='store_false',
+      dest='use_oauth2',
+      default=default_config.use_oauth2,
+      help='Use password instead of OAuth 2.0.')
+  parser.auth_group.add_option(
+      '--no-cookies',
+      action='store_false',
+      dest='save_cookies',
+      default=default_config.save_cookies,
+      help='Do not save authentication cookies to local disk.')
+  parser.auth_group.add_option(
+      '--auth-no-local-webserver',
+      action='store_false',
+      dest='use_local_webserver',
+      default=default_config.use_local_webserver,
+      help='Do not run a local web server when performing OAuth2 login flow.')
+  parser.auth_group.add_option(
+      '--auth-host-port',
+      type=int,
+      default=default_config.webserver_port,
+      help='Port a local web server should listen on. Used only if '
+          '--auth-no-local-webserver is not set. [default: %default]')
+  parser.add_option_group(parser.auth_group)
+
+
+def extract_auth_config_from_options(options):
+  """Given OptionParser parsed options, extracts AuthConfig from it.
+
+  OptionParser should be populated with auth options by 'add_auth_options'.
+  """
+  return make_auth_config(
+      use_oauth2=options.use_oauth2,
+      save_cookies=False if options.use_oauth2 else options.save_cookies,
+      use_local_webserver=options.use_local_webserver,
+      webserver_port=options.auth_host_port)
+
+
+def auth_config_to_command_options(auth_config):
+  """AuthConfig -> list of strings with command line options."""
+  if not auth_config:
+    return []
+  opts = ['--oauth2' if auth_config.use_oauth2 else '--no-oauth2']
+  if not auth_config.save_cookies:
+    opts.append('--no-cookies')
+  if not auth_config.use_local_webserver:
+    opts.append('--auth-no-local-webserver')
+  opts.extend(['--auth-host-port', str(auth_config.webserver_port)])
+  return opts