@classmethod
  @gen.coroutine
  def CreateInvitationURL(cls, client, user_id, identity_key, viewpoint_id, default_url):
    identity_type, identity_value = Identity.SplitKey(identity_key)
    now = util.GetCurrentTimestamp()
    expires = now + Identity._TIME_TO_INVITIATION_EXPIRATION
    encoded_user_id = base64hex.B64HexEncode(util.EncodeVarLengthNumber(user_id), padding=False)
    short_url = yield ShortURL.Create(client,
                                      group_id='pr/%s' % encoded_user_id,
                                      timestamp=now,
                                      expires=expires,
                                      identity_key=identity_key,
                                      viewpoint_id=viewpoint_id,
                                      default_url=default_url,
                                      is_sms=identity_type == 'Phone')

    raise gen.Return(short_url)
Creates and returns a prospective user invitation ShortURL object. The URL is handled
dataset/ETHPy150Open viewfinderco/viewfinder/backend/db/identity.py/Identity.CreateInvitationURL