old_contents: # Copyright 2019 Google LLC All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import sys
  
  from flask import Flask
  app = Flask(__name__)
  
  CERTS = None
  AUDIENCE = None
  
  
  def certs():
      import requests
  
      global CERTS
      if CERTS is None:
          response = requests.get(
              'https://www.gstatic.com/iap/verify/public_key'
          )
          CERTS = response.json()
      return CERTS
  
  
  def get_metadata(item_name):
      import requests
  
      endpoint = 'http://metadata.google.internal'
      path = '/computeMetadata/v1/project/'
      path += item_name
      response = requests.get(
          '{}{}'.format(endpoint, path),
          headers = {'Metadata-Flavor': 'Google'}
      )
      metadata = response.text
      return metadata
  
  
  def audience():
      global AUDIENCE
      if AUDIENCE is None:
          project_number = get_metadata('numeric-project-id')
          project_id = get_metadata('project-id')
          AUDIENCE = '/projects/{}/apps/{}'.format(
              project_number, project_id
          )
      return AUDIENCE
  
  
  def validate_assertion(assertion):
      from jose import jwt
  
      try:
          info = jwt.decode(
              assertion,
              certs(),
              algorithms=['ES256'],
              audience=audience()
              )
          return info['email'], info['sub']
      except Exception as e:
          print('Failed to validate assertion: {}'.format(e), file=sys.stderr)
          return None, None
  
  
  @app.route('/', methods=['GET'])
  def say_hello():
      from flask import request
  
      assertion = request.headers.get('X-Goog-IAP-JWT-Assertion')
      email, id = validate_assertion(assertion)
      page = "<h1>Hello {}</h1>".format(email)
      return page
  
new_contents: # Copyright 2019 Google LLC All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import sys
  
  from flask import Flask
  app = Flask(__name__)
  
  CERTS = None
  AUDIENCE = None
  
  
  def certs():
      """Returns a dictionary of current Google public key certificates for
      validating Google-signed JWTs. Since these change rarely, the result
      is cached on first request for faster subsequent responses.
      """
      import requests
  
      global CERTS
      if CERTS is None:
          response = requests.get(
              'https://www.gstatic.com/iap/verify/public_key'
          )
          CERTS = response.json()
      return CERTS
  
  
  def get_metadata(item_name):
      """Returns a string with the project metadata value for the item_name.
      See https://cloud.google.com/compute/docs/storing-retrieving-metadata for
      possible item_name values.
      """
      import requests
  
      endpoint = 'http://metadata.google.internal'
      path = '/computeMetadata/v1/project/'
      path += item_name
      response = requests.get(
          '{}{}'.format(endpoint, path),
          headers = {'Metadata-Flavor': 'Google'}
      )
      metadata = response.text
      return metadata
  
  
  def audience():
      """Returns the audience value (the JWT 'aud' property) for the current
      running instance. Since this involves a metadata lookup, the result is
      cached when first requested for faster future responses.
      """
      global AUDIENCE
      if AUDIENCE is None:
          project_number = get_metadata('numeric-project-id')
          project_id = get_metadata('project-id')
          AUDIENCE = '/projects/{}/apps/{}'.format(
              project_number, project_id
          )
      return AUDIENCE
  
  
  def validate_assertion(assertion):
      """Checks that the JWT assertion is valid (properly signed, for the
      correct audience) and if so, returns strings for the requesting user's
      email and a persistent user ID. If not valid, returns None for each field.
      """
      from jose import jwt
  
      try:
          info = jwt.decode(
              assertion,
              certs(),
              algorithms=['ES256'],
              audience=audience()
              )
          return info['email'], info['sub']
      except Exception as e:
          print('Failed to validate assertion: {}'.format(e), file=sys.stderr)
          return None, None
  
  
  @app.route('/', methods=['GET'])
  def say_hello():
      from flask import request
  
      assertion = request.headers.get('X-Goog-IAP-JWT-Assertion')
      email, id = validate_assertion(assertion)
      page = "<h1>Hello {}</h1>".format(email)
      return page
  
subject: Add docstring comments to functions