python的模块itsdangerous

这个模块主要用来签名和序列化

使用场景：

一、给字符串添加签名：

　　发送方和接收方拥有相同的密钥--"secret-key",发送方使用密钥对发送内容进行签名，接收方使用相同的密钥对接收到的内容进行验证，看是否是发送方发送的内容

 >>> from itsdangerous import Signer
 >>> s = Signer('secret-key')
 >>> s.sign('my string, ssssssssss,dddddddddddddlsd')
 'my string, ssssssssss,dddddddddddddlsd.nSXTxgO_UMN4gkLZcFCioa-dZSo'
 >>>
 >>> s.unsign('my string, ssssssssss,dddddddddddddlsd.nSXTxgO_UMN4gkLZcFCioa-dZSo')
 'my string, ssssssssss,dddddddddddddlsd'
 >>> s.unsign('my string, ssss.nSXTxgO_UMN4gkLZcFCioa-dZSo')
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/usr/local/lib/python2.7/site-packages/itsdangerous.py", line 374, in unsign
     payload=value)
 itsdangerous.BadSignature: Signature 'nSXTxgO_UMN4gkLZcFCioa-dZSo' does not match
 >>> s.unsign('my string, ssssssssss,dddddddddddddlsd.nSXTxgO_UMN4gkLZcFCioa-dZSP')
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/usr/local/lib/python2.7/site-packages/itsdangerous.py", line 374, in unsign
     payload=value)
 itsdangerous.BadSignature: Signature 'nSXTxgO_UMN4gkLZcFCioa-dZSP' does not match
 >>>

二、带时间戳的签名：

　　签名有一定的时效性，发送方发送时，带上时间信息，接收方判断多长时间内是否失效

>>> from itsdangerous import TimestampSigner
>>> s = TimestampSigner('secret-key')
>>> string = s.sign('foo')
>>> s.unsign(string, max_age=5)
foo
>>> s.unsign(string, max_age=5)
Traceback (most recent call last):
  ...
itsdangerous.SignatureExpired: Signature age 15 > 5 seconds

三、序列化

>>> from itsdangerous import Serializer
>>> s = Serializer('secret-key')
>>> s.dumps([1, 2, 3, 4])
'[1, 2, 3, 4].r7R9RhGgDPvvWl3iNzLuIIfELmo'
And it can of course also load:

>>> s.loads('[1, 2, 3, 4].r7R9RhGgDPvvWl3iNzLuIIfELmo')
[1, 2, 3, 4]
If you want to have the timestamp attached you can use the TimedSerializer.

四、带时间戳的序列化：

>>> from itsdangerous import TimedSerializer
>>> s=TimedSerializer('secret-key')
>>> s.dumps([1,2,3,4])
'[1, 2, 3, 4].DI7WHQ.yVOjwQWau5mVRGuVkoqa7654VXc'
>>> s.loads('[1, 2, 3, 4].DI7WHQ.yVOjwQWau5mVRGuVkoqa7654VXc')
[1, 2, 3, 4]
>>> s.loads('[1, 2, 3, 4].DI7WHQ.yVOjwQWau5mVRGuVkoqa7654VXc',max_age=10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/itsdangerous.py", line 643, in loads
    .unsign(s, max_age, return_timestamp=True)
  File "/usr/local/lib/python2.7/site-packages/itsdangerous.py", line 463, in unsign
    date_signed=self.timestamp_to_datetime(timestamp))
itsdangerous.SignatureExpired: Signature age 28 > 10 seconds
>>> s.loads('[1, 2, 3, 4].DI7WHQ.yVOjwQWau5mVRGuVkoqa7654VXc',max_age=40)
[1, 2, 3, 4]
>>>

五、URL安全序列化

对于限定字符串的场景，你可以使用URL安全序列化

>>> from itsdangerous import URLSafeSerializer
>>> s = URLSafeSerializer('secret-key')
>>> s.dumps([1, 2, 3, 4])
'WzEsMiwzLDRd.wSPHqC0gR7VUqivlSukJ0IeTDgo'
>>> s.loads('WzEsMiwzLDRd.wSPHqC0gR7VUqivlSukJ0IeTDgo')
[1, 2, 3, 4]

六、JSON Web签名

JSON Web Signatures

Starting with “itsdangerous” 0.18 JSON Web Signatures are also supported. They generally work very similar to the already existing URL safe serializer but will emit headers according to the current draft (10) of the JSON Web Signature (JWS) [draft-ietf-jose-json-web-signature].

>>> from itsdangerous import JSONWebSignatureSerializer
>>> s = JSONWebSignatureSerializer('secret-key')
>>> s.dumps({'x': 42})
'eyJhbGciOiJIUzI1NiJ9.eyJ4Ijo0Mn0.ZdTn1YyGz9Yx5B5wNpWRL221G1WpVE5fPCPKNuc6UAo'

When loading the value back the header will not be returned by default like with the other serializers. However it is possible to also ask for the header by passing return_header=True. Custom header fields can be provided upon serialization:

>>> s.dumps(0, header_fields={'v': 1})
'eyJhbGciOiJIUzI1NiIsInYiOjF9.MA.wT-RZI9YU06R919VBdAfTLn82_iIQD70J_j-3F4z_aM'
>>> s.loads('eyJhbGciOiJIUzI1NiIsInYiOjF9.MA.wT-RZI9YU06R919VBdAf'
...         'TLn82_iIQD70J_j-3F4z_aM', return_header=True)
...
(0, {u'alg': u'HS256', u'v': 1})

“itsdangerous” only provides HMAC SHA derivatives and the none algorithm at the moment and does not support the ECC based ones. The algorithm in the header is checked against the one of the serializer and on a mismatch a BadSignatureexception is raised.

七、带时间戳的JSON Web签名

from itsdangerous import TimedJSONWebSignatureSerializer as Serializer
s = Serializer('secret-key', expires_in=60)
s.dumps({'id': user.id}) # user为model中封装过的对象

 

八、盐值

这里的盐值和加密算法里的盐值概念不一样，这里的盐值(salt)可以应用到上面所有情形中，不同的盐值，生成的签名或者序列化的数值不一样

>>> s1 = URLSafeSerializer('secret-key', salt='activate-salt')
>>> s1.dumps(42)
'NDI.kubVFOOugP5PAIfEqLJbXQbfTxs'
>>> s2 = URLSafeSerializer('secret-key', salt='upgrade-salt')
>>> s2.dumps(42)
'NDI.7lx-N1P-z2veJ7nT1_2bnTkjGTE'
>>> s2.loads(s1.dumps(42))
Traceback (most recent call last):
  ...
itsdangerous.BadSignature: Signature "kubVFOOugP5PAIfEqLJbXQbfTxs" does not match
Only the serializer with the same salt can load the value:

>>> s2.loads(s2.dumps(42))
42

九、源码奉上：

 # -*- coding: utf-8 -*-
 """
     itsdangerous
     ~~~~~~~~~~~~

     A module that implements various functions to deal with untrusted
     sources.  Mainly useful for web applications.

     :copyright: (c) 2014 by Armin Ronacher and the Django Software Foundation.
     :license: BSD, see LICENSE for more details.
 """

 import sys
 import hmac
 import zlib
 import time
 import base64
 import hashlib
 import operator
 from datetime import datetime

 PY2 = sys.version_info[0] == 2
 if PY2:
     from itertools import izip
     text_type = unicode
     int_to_byte = chr
     number_types = (int, long, float)
 else:
     from functools import reduce
     izip = zip
     text_type = str
     int_to_byte = operator.methodcaller('to_bytes', 1, 'big')
     number_types = (int, float)

 try:
     import simplejson as json
 except ImportError:
     import json

 class _CompactJSON(object):
     """Wrapper around simplejson that strips whitespace.
     """

     def loads(self, payload):
         return json.loads(payload)

     def dumps(self, obj):
         return json.dumps(obj, separators=(',', ':'))

 compact_json = _CompactJSON()

 # 2011/01/01 in UTC
 EPOCH = 1293840000

 def want_bytes(s, encoding='utf-8', errors='strict'):
     if isinstance(s, text_type):
         s = s.encode(encoding, errors)
     return s

 def is_text_serializer(serializer):
     """Checks wheather a serializer generates text or binary."""
     return isinstance(serializer.dumps({}), text_type)

 # Starting with 3.3 the standard library has a c-implementation for
 # constant time string compares.
 _builtin_constant_time_compare = getattr(hmac, 'compare_digest', None)

 def constant_time_compare(val1, val2):
     """Returns True if the two strings are equal, False otherwise.

     The time taken is independent of the number of characters that match.  Do
     not use this function for anything else than comparision with known
     length targets.

     This is should be implemented in C in order to get it completely right.
     """
     if _builtin_constant_time_compare is not None:
         return _builtin_constant_time_compare(val1, val2)
     len_eq = len(val1) == len(val2)
     if len_eq:
         result = 0
         left = val1
     else:
         result = 1
         left = val2
     for x, y in izip(bytearray(left), bytearray(val2)):
         result |= x ^ y
     return result == 0

 class BadData(Exception):
     """Raised if bad data of any sort was encountered.  This is the
     base for all exceptions that itsdangerous is currently using.

     .. versionadded:: 0.15
     """
     message = None

     def __init__(self, message):
         Exception.__init__(self, message)
         self.message = message

     def __str__(self):
         return text_type(self.message)

     if PY2:
         __unicode__ = __str__
         def __str__(self):
             return self.__unicode__().encode('utf-8')

 class BadPayload(BadData):
     """This error is raised in situations when payload is loaded without
     checking the signature first and an exception happend as a result of
     that.  The original exception that caused that will be stored on the
     exception as :attr:`original_error`.

     This can also happen with a :class:`JSONWebSignatureSerializer` that
     is subclassed and uses a different serializer for the payload than
     the expected one.

     .. versionadded:: 0.15
     """

     def __init__(self, message, original_error=None):
         BadData.__init__(self, message)
         #: If available, the error that indicates why the payload
         #: was not valid.  This might be `None`.
         self.original_error = original_error

 class BadSignature(BadData):
     """This error is raised if a signature does not match.  As of
     itsdangerous 0.14 there are helpful attributes on the exception
     instances.  You can also catch down the baseclass :exc:`BadData`.
     """

     def __init__(self, message, payload=None):
         BadData.__init__(self, message)
         #: The payload that failed the signature test.  In some
         #: situations you might still want to inspect this, even if
         #: you know it was tampered with.
         #:
         #: .. versionadded:: 0.14
         self.payload = payload

 class BadTimeSignature(BadSignature):
     """Raised for time based signatures that fail.  This is a subclass
     of :class:`BadSignature` so you can catch those down as well.
     """

     def __init__(self, message, payload=None, date_signed=None):
         BadSignature.__init__(self, message, payload)

         #: If the signature expired this exposes the date of when the
         #: signature was created.  This can be helpful in order to
         #: tell the user how long a link has been gone stale.
         #:
         #: .. versionadded:: 0.14
         self.date_signed = date_signed

 class BadHeader(BadSignature):
     """Raised if a signed header is invalid in some form.  This only
     happens for serializers that have a header that goes with the
     signature.

     .. versionadded:: 0.24
     """

     def __init__(self, message, payload=None, header=None,
                  original_error=None):
         BadSignature.__init__(self, message, payload)

         #: If the header is actually available but just malformed it
         #: might be stored here.
         self.header = header

         #: If available, the error that indicates why the payload
         #: was not valid.  This might be `None`.
         self.original_error = original_error

 class SignatureExpired(BadTimeSignature):
     """Signature timestamp is older than required max_age.  This is a
     subclass of :exc:`BadTimeSignature` so you can use the baseclass for
     catching the error.
     """

 def base64_encode(string):
     """base64 encodes a single bytestring (and is tolerant to getting
     called with a unicode string).
     The resulting bytestring is safe for putting into URLs.
     """
     string = want_bytes(string)
     return base64.urlsafe_b64encode(string).strip(b'=')

 def base64_decode(string):
     """base64 decodes a single bytestring (and is tolerant to getting
     called with a unicode string).
     The result is also a bytestring.
     """
     string = want_bytes(string, encoding='ascii', errors='ignore')
     return base64.urlsafe_b64decode(string + b'=' * (-len(string) % 4))

 def int_to_bytes(num):
     assert num >= 0
     rv = []
     while num:
         rv.append(int_to_byte(num & 0xff))
         num >>= 8
     return b''.join(reversed(rv))

 def bytes_to_int(bytestr):
     return reduce(lambda a, b: a << 8 | b, bytearray(bytestr), 0)

 class SigningAlgorithm(object):
     """Subclasses of `SigningAlgorithm` have to implement `get_signature` to
     provide signature generation functionality.
     """

     def get_signature(self, key, value):
         """Returns the signature for the given key and value"""
         raise NotImplementedError()

     def verify_signature(self, key, value, sig):
         """Verifies the given signature matches the expected signature"""
         return constant_time_compare(sig, self.get_signature(key, value))

 class NoneAlgorithm(SigningAlgorithm):
     """This class provides a algorithm that does not perform any signing and
     returns an empty signature.
     """

     def get_signature(self, key, value):
         return b''

 class HMACAlgorithm(SigningAlgorithm):
     """This class provides signature generation using HMACs."""

     #: The digest method to use with the MAC algorithm.  This defaults to sha1
     #: but can be changed for any other function in the hashlib module.
     default_digest_method = staticmethod(hashlib.sha1)

     def __init__(self, digest_method=None):
         if digest_method is None:
             digest_method = self.default_digest_method
         self.digest_method = digest_method

     def get_signature(self, key, value):
         mac = hmac.new(key, msg=value, digestmod=self.digest_method)
         return mac.digest()

 class Signer(object):
     """This class can sign bytes and unsign it and validate the signature
     provided.

     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 where the same
     signed value in one part can mean something different in another part
     is a security risk.

     See :ref:`the-salt` for an example of what the salt is doing and how you
     can utilize it.

     .. versionadded:: 0.14
        `key_derivation` and `digest_method` were added as arguments to the
        class constructor.

     .. versionadded:: 0.18
         `algorithm` was added as an argument to the class constructor.
     """

     #: The digest method to use for the signer.  This defaults to sha1 but can
     #: be changed for any other function in the hashlib module.
     #:
     #: .. versionchanged:: 0.14
     default_digest_method = staticmethod(hashlib.sha1)

     #: Controls how the key is derived.  The default is Django style
     #: concatenation.  Possible values are ``concat``, ``django-concat``
     #: and ``hmac``.  This is used for deriving a key from the secret key
     #: with an added salt.
     #:
     #: .. versionadded:: 0.14
     default_key_derivation = 'django-concat'

     def __init__(self, secret_key, salt=None, sep='.', key_derivation=None,
                  digest_method=None, algorithm=None):
         self.secret_key = want_bytes(secret_key)
         self.sep = sep
         self.salt = 'itsdangerous.Signer' if salt is None else salt
         if key_derivation is None:
             key_derivation = self.default_key_derivation
         self.key_derivation = key_derivation
         if digest_method is None:
             digest_method = self.default_digest_method
         self.digest_method = digest_method
         if algorithm is None:
             algorithm = HMACAlgorithm(self.digest_method)
         self.algorithm = algorithm

     def derive_key(self):
         """This method is called to derive the key.  If you're unhappy with
         the default key derivation choices you can override them here.
         Keep in mind that the key derivation in itsdangerous is not intended
         to be used as a security method to make a complex key out of a short
         password.  Instead you should use large random secret keys.
         """
         salt = want_bytes(self.salt)
         if self.key_derivation == 'concat':
             return self.digest_method(salt + self.secret_key).digest()
         elif self.key_derivation == 'django-concat':
             return self.digest_method(salt + b'signer' +
                 self.secret_key).digest()
         elif self.key_derivation == 'hmac':
             mac = hmac.new(self.secret_key, digestmod=self.digest_method)
             mac.update(salt)
             return mac.digest()
         elif self.key_derivation == 'none':
             return self.secret_key
         else:
             raise TypeError('Unknown key derivation method')

     def get_signature(self, value):
         """Returns the signature for the given value"""
         value = want_bytes(value)
         key = self.derive_key()
         sig = self.algorithm.get_signature(key, value)
         return base64_encode(sig)

     def sign(self, value):
         """Signs the given string."""
         return value + want_bytes(self.sep) + self.get_signature(value)

     def verify_signature(self, value, sig):
         """Verifies the signature for the given value."""
         key = self.derive_key()
         try:
             sig = base64_decode(sig)
         except Exception:
             return False
         return self.algorithm.verify_signature(key, value, sig)

     def unsign(self, signed_value):
         """Unsigns the given string."""
         signed_value = want_bytes(signed_value)
         sep = want_bytes(self.sep)
         if sep not in signed_value:
             raise BadSignature('No %r found in value' % self.sep)
         value, sig = signed_value.rsplit(sep, 1)
         if self.verify_signature(value, sig):
             return value
         raise BadSignature('Signature %r does not match' % sig,
                            payload=value)

     def validate(self, signed_value):
         """Just validates the given signed value.  Returns `True` if the
         signature exists and is valid, `False` otherwise."""
         try:
             self.unsign(signed_value)
             return True
         except BadSignature:
             return False

 class TimestampSigner(Signer):
     """Works like the regular :class:`Signer` but also records the time
     of the signing and can be used to expire signatures.  The unsign
     method can rause a :exc:`SignatureExpired` method if the unsigning
     failed because the signature is expired.  This exception is a subclass
     of :exc:`BadSignature`.
     """

     def get_timestamp(self):
         """Returns the current timestamp.  This implementation returns the
         seconds since 1/1/2011.  The function must return an integer.
         """
         return int(time.time() - EPOCH)

     def timestamp_to_datetime(self, ts):
         """Used to convert the timestamp from `get_timestamp` into a
         datetime object.
         """
         return datetime.utcfromtimestamp(ts + EPOCH)

     def sign(self, value):
         """Signs the given string and also attaches a time information."""
         value = want_bytes(value)
         timestamp = base64_encode(int_to_bytes(self.get_timestamp()))
         sep = want_bytes(self.sep)
         value = value + sep + timestamp
         return value + sep + self.get_signature(value)

     def unsign(self, value, max_age=None, return_timestamp=False):
         """Works like the regular :meth:`~Signer.unsign` but can also
         validate the time.  See the base docstring of the class for
         the general behavior.  If `return_timestamp` is set to `True`
         the timestamp of the signature will be returned as naive
         :class:`datetime.datetime` object in UTC.
         """
         try:
             result = Signer.unsign(self, value)
             sig_error = None
         except BadSignature as e:
             sig_error = e
             result = e.payload or b''
         sep = want_bytes(self.sep)

         # If there is no timestamp in the result there is something
         # seriously wrong.  In case there was a signature error, we raise
         # that one directly, otherwise we have a weird situation in which
         # we shouldn't have come except someone uses a time-based serializer
         # on non-timestamp data, so catch that.
         if not sep in result:
             if sig_error:
                 raise sig_error
             raise BadTimeSignature('timestamp missing', payload=result)

         value, timestamp = result.rsplit(sep, 1)
         try:
             timestamp = bytes_to_int(base64_decode(timestamp))
         except Exception:
             timestamp = None

         # Signature is *not* okay.  Raise a proper error now that we have
         # split the value and the timestamp.
         if sig_error is not None:
             raise BadTimeSignature(text_type(sig_error), payload=value,
                                    date_signed=timestamp)

         # Signature was okay but the timestamp is actually not there or
         # malformed.  Should not happen, but well.  We handle it nonetheless
         if timestamp is None:
             raise BadTimeSignature('Malformed timestamp', payload=value)

         # Check timestamp is not older than max_age
         if max_age is not None:
             age = self.get_timestamp() - timestamp
             if age > max_age:
                 raise SignatureExpired(
                     'Signature age %s > %s seconds' % (age, max_age),
                     payload=value,
                     date_signed=self.timestamp_to_datetime(timestamp))

         if return_timestamp:
             return value, self.timestamp_to_datetime(timestamp)
         return value

     def validate(self, signed_value, max_age=None):
         """Just validates the given signed value.  Returns `True` if the
         signature exists and is valid, `False` otherwise."""
         try:
             self.unsign(signed_value, max_age=max_age)
             return True
         except BadSignature:
             return False

 class Serializer(object):
     """This class provides a serialization interface on top of the
     signer.  It provides a similar API to json/pickle and other modules but is
     slightly differently structured internally.  If you want to change the
     underlying implementation for parsing and loading you have to override the
     :meth:`load_payload` and :meth:`dump_payload` functions.

     This implementation uses simplejson if available for dumping and loading
     and will fall back to the standard library's json module if it's not
     available.

     Starting with 0.14 you do not need to subclass this class in order to
     switch out or customer the :class:`Signer`.  You can instead also pass a
     different class to the constructor as well as keyword arguments as
     dictionary that should be forwarded::

         s = Serializer(signer_kwargs={'key_derivation': 'hmac'})

     .. versionchanged:: 0.14:
        The `signer` and `signer_kwargs` parameters were added to the
        constructor.
     """

     #: If a serializer module or class is not passed to the constructor
     #: this one is picked up.  This currently defaults to :mod:`json`.
     default_serializer = json

     #: The default :class:`Signer` class that is being used by this
     #: serializer.
     #:
     #: .. versionadded:: 0.14
     default_signer = Signer

     def __init__(self, secret_key, salt=b'itsdangerous', serializer=None,
                  signer=None, signer_kwargs=None):
         self.secret_key = want_bytes(secret_key)
         self.salt = want_bytes(salt)
         if serializer is None:
             serializer = self.default_serializer
         self.serializer = serializer
         self.is_text_serializer = is_text_serializer(serializer)
         if signer is None:
             signer = self.default_signer
         self.signer = signer
         self.signer_kwargs = signer_kwargs or {}

     def load_payload(self, payload, serializer=None):
         """Loads the encoded object.  This function raises :class:`BadPayload`
         if the payload is not valid.  The `serializer` parameter can be used to
         override the serializer stored on the class.  The encoded payload is
         always byte based.
         """
         if serializer is None:
             serializer = self.serializer
             is_text = self.is_text_serializer
         else:
             is_text = is_text_serializer(serializer)
         try:
             if is_text:
                 payload = payload.decode('utf-8')
             return serializer.loads(payload)
         except Exception as e:
             raise BadPayload('Could not load the payload because an '
                 'exception occurred on unserializing the data',
                 original_error=e)

     def dump_payload(self, obj):
         """Dumps the encoded object.  The return value is always a
         bytestring.  If the internal serializer is text based the value
         will automatically be encoded to utf-8.
         """
         return want_bytes(self.serializer.dumps(obj))

     def make_signer(self, salt=None):
         """A method that creates a new instance of the signer to be used.
         The default implementation uses the :class:`Signer` baseclass.
         """
         if salt is None:
             salt = self.salt
         return self.signer(self.secret_key, salt=salt, **self.signer_kwargs)

     def dumps(self, obj, salt=None):
         """Returns a signed string serialized with the internal serializer.
         The return value can be either a byte or unicode string depending
         on the format of the internal serializer.
         """
         payload = want_bytes(self.dump_payload(obj))
         rv = self.make_signer(salt).sign(payload)
         if self.is_text_serializer:
             rv = rv.decode('utf-8')
         return rv

     def dump(self, obj, f, salt=None):
         """Like :meth:`dumps` but dumps into a file.  The file handle has
         to be compatible with what the internal serializer expects.
         """
         f.write(self.dumps(obj, salt))

     def loads(self, s, salt=None):
         """Reverse of :meth:`dumps`, raises :exc:`BadSignature` if the
         signature validation fails.
         """
         s = want_bytes(s)
         return self.load_payload(self.make_signer(salt).unsign(s))

     def load(self, f, salt=None):
         """Like :meth:`loads` but loads from a file."""
         return self.loads(f.read(), salt)

     def loads_unsafe(self, s, salt=None):
         """Like :meth:`loads` but without verifying the signature.  This is
         potentially very dangerous to use depending on how your serializer
         works.  The return value is ``(signature_okay, payload)`` instead of
         just the payload.  The first item will be a boolean that indicates
         if the signature is okay (``True``) or if it failed.  This function
         never fails.

         Use it for debugging only and if you know that your serializer module
         is not exploitable (eg: do not use it with a pickle serializer).

         .. versionadded:: 0.15
         """
         return self._loads_unsafe_impl(s, salt)

     def _loads_unsafe_impl(self, s, salt, load_kwargs=None,
                            load_payload_kwargs=None):
         """Lowlevel helper function to implement :meth:`loads_unsafe` in
         serializer subclasses.
         """
         try:
             return True, self.loads(s, salt=salt, **(load_kwargs or {}))
         except BadSignature as e:
             if e.payload is None:
                 return False, None
             try:
                 return False, self.load_payload(e.payload,
                     **(load_payload_kwargs or {}))
             except BadPayload:
                 return False, None

     def load_unsafe(self, f, *args, **kwargs):
         """Like :meth:`loads_unsafe` but loads from a file.

         .. versionadded:: 0.15
         """
         return self.loads_unsafe(f.read(), *args, **kwargs)

 class TimedSerializer(Serializer):
     """Uses the :class:`TimestampSigner` instead of the default
     :meth:`Signer`.
     """

     default_signer = TimestampSigner

     def loads(self, s, max_age=None, return_timestamp=False, salt=None):
         """Reverse of :meth:`dumps`, raises :exc:`BadSignature` if the
         signature validation fails.  If a `max_age` is provided it will
         ensure the signature is not older than that time in seconds.  In
         case the signature is outdated, :exc:`SignatureExpired` is raised
         which is a subclass of :exc:`BadSignature`.  All arguments are
         forwarded to the signer's :meth:`~TimestampSigner.unsign` method.
         """
         base64d, timestamp = self.make_signer(salt) \
             .unsign(s, max_age, return_timestamp=True)
         payload = self.load_payload(base64d)
         if return_timestamp:
             return payload, timestamp
         return payload

     def loads_unsafe(self, s, max_age=None, salt=None):
         load_kwargs = {'max_age': max_age}
         load_payload_kwargs = {}
         return self._loads_unsafe_impl(s, salt, load_kwargs, load_payload_kwargs)

 class JSONWebSignatureSerializer(Serializer):
     """This serializer implements JSON Web Signature (JWS) support.  Only
     supports the JWS Compact Serialization.
     """

     jws_algorithms = {
         'HS256': HMACAlgorithm(hashlib.sha256),
         'HS384': HMACAlgorithm(hashlib.sha384),
         'HS512': HMACAlgorithm(hashlib.sha512),
         'none': NoneAlgorithm(),
     }

     #: The default algorithm to use for signature generation
     default_algorithm = 'HS256'

     default_serializer = compact_json

     def __init__(self, secret_key, salt=None, serializer=None,
                  signer=None, signer_kwargs=None, algorithm_name=None):
         Serializer.__init__(self, secret_key, salt, serializer,
                             signer, signer_kwargs)
         if algorithm_name is None:
             algorithm_name = self.default_algorithm
         self.algorithm_name = algorithm_name
         self.algorithm = self.make_algorithm(algorithm_name)

     def load_payload(self, payload, return_header=False):
         payload = want_bytes(payload)
         if b'.' not in payload:
             raise BadPayload('No "." found in value')
         base64d_header, base64d_payload = payload.split(b'.', 1)
         try:
             json_header = base64_decode(base64d_header)
         except Exception as e:
             raise BadHeader('Could not base64 decode the header because of '
                 'an exception', original_error=e)
         try:
             json_payload = base64_decode(base64d_payload)
         except Exception as e:
             raise BadPayload('Could not base64 decode the payload because of '
                 'an exception', original_error=e)
         try:
             header = Serializer.load_payload(self, json_header,
                 serializer=json)
         except BadData as e:
             raise BadHeader('Could not unserialize header because it was '
                 'malformed', original_error=e)
         if not isinstance(header, dict):
             raise BadHeader('Header payload is not a JSON object',
                 header=header)
         payload = Serializer.load_payload(self, json_payload)
         if return_header:
             return payload, header
         return payload

     def dump_payload(self, header, obj):
         base64d_header = base64_encode(self.serializer.dumps(header))
         base64d_payload = base64_encode(self.serializer.dumps(obj))
         return base64d_header + b'.' + base64d_payload

     def make_algorithm(self, algorithm_name):
         try:
             return self.jws_algorithms[algorithm_name]
         except KeyError:
             raise NotImplementedError('Algorithm not supported')

     def make_signer(self, salt=None, algorithm=None):
         if salt is None:
             salt = self.salt
         key_derivation = 'none' if salt is None else None
         if algorithm is None:
             algorithm = self.algorithm
         return self.signer(self.secret_key, salt=salt, sep='.',
             key_derivation=key_derivation, algorithm=algorithm)

     def make_header(self, header_fields):
         header = header_fields.copy() if header_fields else {}
         header['alg'] = self.algorithm_name
         return header

     def dumps(self, obj, salt=None, header_fields=None):
         """Like :meth:`~Serializer.dumps` but creates a JSON Web Signature.  It
         also allows for specifying additional fields to be included in the JWS
         Header.
         """
         header = self.make_header(header_fields)
         signer = self.make_signer(salt, self.algorithm)
         return signer.sign(self.dump_payload(header, obj))

     def loads(self, s, salt=None, return_header=False):
         """Reverse of :meth:`dumps`. If requested via `return_header` it will
         return a tuple of payload and header.
         """
         payload, header = self.load_payload(
             self.make_signer(salt, self.algorithm).unsign(want_bytes(s)),
             return_header=True)
         if header.get('alg') != self.algorithm_name:
             raise BadHeader('Algorithm mismatch', header=header,
                             payload=payload)
         if return_header:
             return payload, header
         return payload

     def loads_unsafe(self, s, salt=None, return_header=False):
         kwargs = {'return_header': return_header}
         return self._loads_unsafe_impl(s, salt, kwargs, kwargs)

 class TimedJSONWebSignatureSerializer(JSONWebSignatureSerializer):
     """Works like the regular :class:`JSONWebSignatureSerializer` but also
     records the time of the signing and can be used to expire signatures.

     JWS currently does not specify this behavior but it mentions a possibility
     extension like this in the spec.  Expiry date is encoded into the header
     similarily as specified in `draft-ietf-oauth-json-web-token
     <http://self-issued.info/docs/draft-ietf-oauth-json-web-token.html#expDef`_.

     The unsign method can raise a :exc:`SignatureExpired` method if the
     unsigning failed because the signature is expired.  This exception is a
     subclass of :exc:`BadSignature`.
     """

     DEFAULT_EXPIRES_IN = 3600

     def __init__(self, secret_key, expires_in=None, **kwargs):
         JSONWebSignatureSerializer.__init__(self, secret_key, **kwargs)
         if expires_in is None:
             expires_in = self.DEFAULT_EXPIRES_IN
         self.expires_in = expires_in

     def make_header(self, header_fields):
         header = JSONWebSignatureSerializer.make_header(self, header_fields)
         iat = self.now()
         exp = iat + self.expires_in
         header['iat'] = iat
         header['exp'] = exp
         return header

     def loads(self, s, salt=None, return_header=False):
         payload, header = JSONWebSignatureSerializer.loads(
             self, s, salt, return_header=True)

         if 'exp' not in header:
             raise BadSignature('Missing expiry date', payload=payload)

         if not (isinstance(header['exp'], number_types)
                 and header['exp'] > 0):
             raise BadSignature('expiry date is not an IntDate',
                                payload=payload)

         if header['exp'] < self.now():
             raise SignatureExpired('Signature expired', payload=payload,
                                    date_signed=self.get_issue_date(header))

         if return_header:
             return payload, header
         return payload

     def get_issue_date(self, header):
         rv = header.get('iat')
         if isinstance(rv, number_types):
             return datetime.utcfromtimestamp(int(rv))

     def now(self):
         return int(time.time())

 class URLSafeSerializerMixin(object):
     """Mixed in with a regular serializer it will attempt to zlib compress
     the string to make it shorter if necessary.  It will also base64 encode
     the string so that it can safely be placed in a URL.
     """

     def load_payload(self, payload):
         decompress = False
         if payload.startswith(b'.'):
             payload = payload[1:]
             decompress = True
         try:
             json = base64_decode(payload)
         except Exception as e:
             raise BadPayload('Could not base64 decode the payload because of '
                 'an exception', original_error=e)
         if decompress:
             try:
                 json = zlib.decompress(json)
             except Exception as e:
                 raise BadPayload('Could not zlib decompress the payload before '
                     'decoding the payload', original_error=e)
         return super(URLSafeSerializerMixin, self).load_payload(json)

     def dump_payload(self, obj):
         json = super(URLSafeSerializerMixin, self).dump_payload(obj)
         is_compressed = False
         compressed = zlib.compress(json)
         if len(compressed) < (len(json) - 1):
             json = compressed
             is_compressed = True
         base64d = base64_encode(json)
         if is_compressed:
             base64d = b'.' + base64d
         return base64d

 class URLSafeSerializer(URLSafeSerializerMixin, Serializer):
     """Works like :class:`Serializer` but dumps and loads into a URL
     safe string consisting of the upper and lowercase character of the
     alphabet as well as ``'_'``, ``'-'`` and ``'.'``.
     """
     default_serializer = compact_json

 class URLSafeTimedSerializer(URLSafeSerializerMixin, TimedSerializer):
     """Works like :class:`TimedSerializer` but dumps and loads into a URL
     safe string consisting of the upper and lowercase character of the
     alphabet as well as ``'_'``, ``'-'`` and ``'.'``.
     """
     default_serializer = compact_json

itsdangerous.py

refer:

1、https://pythonhosted.org/itsdangerous/

2、http://itsdangerous.readthedocs.io/en/latest/

3、http://cxymrzero.github.io/blog/2015/03/18/flask-token/