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//usr/lib/python2.7/site-packages/itsdangerous/jws.py

import hashlib
import time
from datetime import datetime

from ._compat import number_types
from ._json import _CompactJSON
from ._json import json
from .encoding import base64_decode
from .encoding import base64_encode
from .encoding import want_bytes
from .exc import BadData
from .exc import BadHeader
from .exc import BadPayload
from .exc import BadSignature
from .exc import SignatureExpired
from .serializer import Serializer
from .signer import HMACAlgorithm
from .signer import NoneAlgorithm

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 = "HS512"

default_serializer = _CompactJSON

def __init__(
        self,
        secret_key,
        salt=None,
        serializer=None,
        serializer_kwargs=None,
        signer=None,
        signer_kwargs=None,
        algorithm_name=None,
    ):
        Serializer.__init__(
            self,
            secret_key=secret_key,
            salt=salt,
            serializer=serializer,
            serializer_kwargs=serializer_kwargs,
            signer=signer,
            signer_kwargs=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, serializer=None, 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, serializer=serializer)
        if return_header:
            return payload, header
        return payload

def dump_payload(self, header, obj):
        base64d_header = base64_encode(
            self.serializer.dumps(header, **self.serializer_kwargs)
        )
        base64d_payload = base64_encode(
            self.serializer.dumps(obj, **self.serializer_kwargs)
        )
        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
    possible extension like this in the spec. Expiry date is encoded
    into the header similar to what's specified in `draft-ietf-oauth
    -json-web-token <http://self-issued.info/docs/draft-ietf-oauth-json
    -web-token.html#expDef>`_.
    """

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)

int_date_error = BadHeader("Expiry date is not an IntDate", payload=payload)
        try:
            header["exp"] = int(header["exp"])
        except ValueError:
            raise int_date_error
        if header["exp"] < 0:
            raise int_date_error

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())