text: """
  Functions for creating and restoring url-safe signed JSON objects.
  
  The format used looks like this:
  
  >>> signing.dumps("hello")
  'ImhlbGxvIg:1QaUZC:YIye-ze3TTx7gtSv422nZA4sgmk'
  
  There are two components here, separated by a ':'. The first component is a
  URLsafe base64 encoded JSON of the object passed to dumps(). The second
  component is a base64 encoded hmac/SHA1 hash of "$first_component:$secret"
  
  signing.loads(s) checks the signature and returns the deserialized object.
  If the signature fails, a BadSignature exception is raised.
  
  >>> signing.loads("ImhlbGxvIg:1QaUZC:YIye-ze3TTx7gtSv422nZA4sgmk")
  'hello'
  >>> signing.loads("ImhlbGxvIg:1QaUZC:YIye-ze3TTx7gtSv422nZA4sgmk-modified")
  ...
  BadSignature: Signature failed: ImhlbGxvIg:1QaUZC:YIye-ze3TTx7gtSv422nZA4sgmk-modified
  
  You can optionally compress the JSON prior to base64 encoding it to save
  space, using the compress=True argument. This checks if compression actually
  helps and only applies compression if the result is a shorter string:
  
  >>> signing.dumps(list(range(1, 20)), compress=True)
  '.eJwFwcERACAIwLCF-rCiILN47r-GyZVJsNgkxaFxoDgxcOHGxMKD_T7vhAml:1QaUaL:BA0thEZrp4FQVXIXuOvYJtLJSrQ'
  
  The fact that the string is compressed is signalled by the prefixed '.' at the
  start of the base64 JSON.
  
  There are 65 url-safe characters: the 64 used by url-safe base64 and the ':'.
  These functions make use of all of them.
  """
  
  import base64
  import datetime
  import json
  import time
  import zlib
  
  from django.conf import settings
  from django.utils import baseconv
  from django.utils.crypto import constant_time_compare, salted_hmac
  from django.utils.encoding import force_bytes
  from django.utils.module_loading import import_string
  from django.utils.regex_helper import _lazy_re_compile
  
  _SEP_UNSAFE = _lazy_re_compile(r'^[A-z0-9-_=]*$')
  
  
  class BadSignature(Exception):
      """Signature does not match."""
      pass
  
  
  class SignatureExpired(BadSignature):
      """Signature timestamp is older than required max_age."""
      pass
  
  
  def b64_encode(s):
      return base64.urlsafe_b64encode(s).strip(b'=')
  
  
  def b64_decode(s):
      pad = b'=' * (-len(s) % 4)
      return base64.urlsafe_b64decode(s + pad)
  
  
  def base64_hmac(salt, value, key):
      return b64_encode(salted_hmac(salt, value, key).digest()).decode()
  
  
  def get_cookie_signer(salt='django.core.signing.get_cookie_signer'):
      Signer = import_string(settings.SIGNING_BACKEND)
      key = force_bytes(settings.SECRET_KEY)  # SECRET_KEY may be str or bytes.
      return Signer(b'django.http.cookies' + key, salt=salt)
  
  
  class JSONSerializer:
      """
      Simple wrapper around json to be used in signing.dumps and
      signing.loads.
      """
      def dumps(self, obj):
          return json.dumps(obj, separators=(',', ':')).encode('latin-1')
  
      def loads(self, data):
          return json.loads(data.decode('latin-1'))
  
  
  def dumps(obj, key=None, salt='django.core.signing', serializer=JSONSerializer, compress=False):
      """
      Return URL-safe, hmac/SHA1 signed base64 compressed JSON string. If key is
      None, use settings.SECRET_KEY instead.
  
      If compress is True (not the default), check if compressing using zlib can
      save some space. Prepend a '.' to signify compression. This is included
      in the signature, to protect against zip bombs.
  
      Salt can be used to namespace the hash, so that a signed string is
      only valid for a given namespace. Leaving this at the default
      value or re-using a salt value across different parts of your
      application without good cause is a security risk.
  
      The serializer is expected to return a bytestring.
      """
      data = serializer().dumps(obj)
  
      # Flag for if it's been compressed or not
      is_compressed = False
  
      if compress:
          # Avoid zlib dependency unless compress is being used
          compressed = zlib.compress(data)
          if len(compressed) < (len(data) - 1):
              data = compressed
              is_compressed = True
      base64d = b64_encode(data).decode()
      if is_compressed:
          base64d = '.' + base64d
      return TimestampSigner(key, salt=salt).sign(base64d)
  
  
  def loads(s, key=None, salt='django.core.signing', serializer=JSONSerializer, max_age=None):
      """
      Reverse of dumps(), raise BadSignature if signature fails.
  
      The serializer is expected to accept a bytestring.
      """
      # TimestampSigner.unsign() returns str but base64 and zlib compression
      # operate on bytes.
      base64d = TimestampSigner(key, salt=salt).unsign(s, max_age=max_age).encode()
      decompress = base64d[:1] == b'.'
      if decompress:
          # It's compressed; uncompress it first
          base64d = base64d[1:]
      data = b64_decode(base64d)
      if decompress:
          data = zlib.decompress(data)
      return serializer().loads(data)
  
  
  class Signer:
  
      def __init__(self, key=None, sep=':', salt=None):
          # Use of native strings in all versions of Python
          self.key = key or settings.SECRET_KEY
          self.sep = sep
          if _SEP_UNSAFE.match(self.sep):
              raise ValueError(
                  'Unsafe Signer separator: %r (cannot be empty or consist of '
                  'only A-z0-9-_=)' % sep,
              )
          self.salt = salt or '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
  
      def signature(self, value):
          return base64_hmac(self.salt + 'signer', value, self.key)
  
      def sign(self, value):
          return '%s%s%s' % (value, self.sep, self.signature(value))
  
      def unsign(self, signed_value):
          if self.sep not in signed_value:
              raise BadSignature('No "%s" found in value' % self.sep)
          value, sig = signed_value.rsplit(self.sep, 1)
          if constant_time_compare(sig, self.signature(value)):
              return value
          raise BadSignature('Signature "%s" does not match' % sig)
  
  
  class TimestampSigner(Signer):
  
      def timestamp(self):
          return baseconv.base62.encode(int(time.time()))
  
      def sign(self, value):
          value = '%s%s%s' % (value, self.sep, self.timestamp())
          return super().sign(value)
  
      def unsign(self, value, max_age=None):
          """
          Retrieve original value and check it wasn't signed more
          than max_age seconds ago.
          """
          result = super().unsign(value)
          value, timestamp = result.rsplit(self.sep, 1)
          timestamp = baseconv.base62.decode(timestamp)
          if max_age is not None:
              if isinstance(max_age, datetime.timedelta):
                  max_age = max_age.total_seconds()
              # Check timestamp is not older than max_age
              age = time.time() - timestamp
              if age > max_age:
                  raise SignatureExpired(
                      'Signature age %s > %s seconds' % (age, max_age))
          return value
  