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"""ACME-specific JWS.
The JWS implementation in josepy only implements the base JOSE standard. In
order to support the new header fields defined in ACME, this module defines some
ACME-specific classes that layer on top of josepy.
"""
from typing import Optional
import josepy as jose
class Header(jose.Header):
"""ACME-specific JOSE Header. Implements nonce, kid, and url.
"""
nonce = jose.Field('nonce', omitempty=True, encoder=jose.encode_b64jose)
kid = jose.Field('kid', omitempty=True)
url = jose.Field('url', omitempty=True)
# Mypy does not understand the josepy magic happening here, and falsely claims
# that nonce is redefined. Let's ignore the type check here.
@nonce.decoder # type: ignore
def nonce(value: str) -> bytes: # pylint: disable=no-self-argument,missing-function-docstring
try:
return jose.decode_b64jose(value)
except jose.DeserializationError as error:
# TODO: custom error
raise jose.DeserializationError("Invalid nonce: {0}".format(error))
class Signature(jose.Signature):
"""ACME-specific Signature. Uses ACME-specific Header for customer fields."""
__slots__ = jose.Signature._orig_slots # pylint: disable=no-member
# TODO: decoder/encoder should accept cls? Otherwise, subclassing
# JSONObjectWithFields is tricky...
header_cls = Header
header = jose.Field(
'header', omitempty=True, default=header_cls(),
decoder=header_cls.from_json)
# TODO: decoder should check that nonce is in the protected header
class JWS(jose.JWS):
"""ACME-specific JWS. Includes none, url, and kid in protected header."""
signature_cls = Signature
__slots__ = jose.JWS._orig_slots
@classmethod
# pylint: disable=arguments-differ
def sign(cls, payload: bytes, key: jose.JWK, alg: jose.JWASignature, nonce: Optional[bytes],
url: Optional[str] = None, kid: Optional[str] = None) -> jose.JWS:
# Per ACME spec, jwk and kid are mutually exclusive, so only include a
# jwk field if kid is not provided.
include_jwk = kid is None
return super().sign(payload, key=key, alg=alg,
protect=frozenset(['nonce', 'url', 'kid', 'jwk', 'alg']),
nonce=nonce, url=url, kid=kid,
include_jwk=include_jwk)
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