text: # Copyright 2016, Google Inc.
  # All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions are
  # met:
  #
  #     * Redistributions of source code must retain the above copyright
  # notice, this list of conditions and the following disclaimer.
  #     * Redistributions in binary form must reproduce the above
  # copyright notice, this list of conditions and the following disclaimer
  # in the documentation and/or other materials provided with the
  # distribution.
  #     * Neither the name of Google Inc. nor the names of its
  # contributors may be used to endorse or promote products derived from
  # this software without specific prior written permission.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  """Provides gRPC authentication support using google.auth."""
  
  from __future__ import absolute_import
  
  import google.auth
  import google.auth.credentials
  import google.auth.transport.grpc
  
  try:
      import google.auth.transport.requests
      # pylint: disable=invalid-name
      # Pylint recognizes this as a class, but we're aliasing it as a factory
      # function.
      _request_factory = google.auth.transport.requests.Request
      # pylint: enable=invalid-name
  except ImportError:
      try:
          import httplib2
          import google_auth_httplib2
  
          def _request_factory():
              http = httplib2.Http()
              return google_auth_httplib2.Request(http)
  
      except ImportError:
          raise ImportError(
              'No HTTP transport is available. Please install requests or '
              'httplib2 and google_auth_httplib2.')
  
  
  def get_default_credentials(scopes):
      """Gets the Application Default Credentials."""
      credentials, _ = google.auth.default(scopes=scopes)
      return credentials
  
  
  def secure_authorized_channel(
          credentials, target, ssl_credentials=None):
      """Creates a secure authorized gRPC channel."""
      http_request = _request_factory()
      return google.auth.transport.grpc.secure_authorized_channel(
          credentials, http_request, target,
          ssl_credentials=ssl_credentials)
  