text: #    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 base64
  import os
  import shutil
  import subprocess
  import uuid
  from tempfile import mkdtemp
  
  
  def random_uuid():
      return uuid.uuid4().hex
  
  
  def dash_uuid(id):
      return str(uuid.UUID(id, version=4))
  
  
  def canonical_uuid_string(id):
      return uuid.UUID(id, version=4).hex
  
  
  def datetime_to_string(dt):
      return dt.strftime("%Y-%m-%dT%H:%M:%S.%f")
  
  
  def generateCert(auth_key, entity_key, user=True, principal_list=[], serial=0,
                   days_valid=180, identity=''):
      # Temporarily write the authority private key, entity public key to files
      temp_dir = mkdtemp()
      ca_file = '/'.join([temp_dir, 'ca_key'])
      pub_file = '/'.join([temp_dir, 'entity.pub'])
      cert_file = '/'.join([temp_dir, 'entity-cert.pub'])
      cert = ''
      try:
          fd = os.open(ca_file, os.O_WRONLY | os.O_CREAT, 0o600)
          os.close(fd)
          with open(ca_file, "w") as text_file:
              text_file.write(auth_key)
          with open(pub_file, "w", 0o644) as text_file:
              text_file.write(entity_key)
          args = ['ssh-keygen', '-s', ca_file,
                  '-V', '-1d:+{}d'.format(days_valid)]
          if serial:
              args.extend(['-z', str(serial)])
          if identity:
              args.extend(['-I', '{}_{}'.format(identity, serial)])
          if principal_list:
              args.extend(['-n', ','.join(principal_list)])
          if not user:
              args.append('-h')
          args.append(pub_file)
          subprocess.check_output(args, stderr=subprocess.STDOUT)
          # Read the contents of the certificate file
          with open(cert_file, 'r') as text_file:
              cert = text_file.read().strip('\n')
      finally:
          shutil.rmtree(temp_dir)
      return cert
  
  
  def revokedKeysBase64(ca_public, serial_list):
      # Temporarily write the authority private key and list of serials
      temp_dir = mkdtemp()
      ca_file = '/'.join([temp_dir, 'ca_public'])
      serials_file =  '/'.join([temp_dir, 'serials'])
      revoked_file = '/'.join([temp_dir, 'revoked'])
      try:
          with open(ca_file, "w", 0o644) as text_file:
              text_file.write(ca_public)
          with open(serials_file, "w", 0o644) as text_file:
              for s in serial_list:
                  text_file.write("serial: {}\n".format(s))
          args = ['ssh-keygen', '-k', '-f', revoked_file, '-s', ca_file, serials_file]
          subprocess.check_output(args, stderr=subprocess.STDOUT)
          # Return the base64 encoded contents of the revoked keys file
          with open(revoked_file, 'r') as text_file:
              b64data = base64.b64encode(text_file.read())
      finally:
          shutil.rmtree(temp_dir)
      return b64data
  