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dist/ba_data/python-site-packages/py_vapid/jwt.py

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+import binascii
+import json
+
+from cryptography.exceptions import InvalidSignature
+from cryptography.hazmat.primitives.asymmetric import ec, utils
+from cryptography.hazmat.primitives import hashes
+
+from py_vapid.utils import b64urldecode, b64urlencode, num_to_bytes
+
+
+def extract_signature(auth):
+    """Extracts the payload and signature from a JWT, converting from RFC7518
+    to RFC 3279
+
+    :param auth: A JWT Authorization Token.
+    :type auth: str
+
+    :return tuple containing the signature material and signature
+
+    """
+    payload, asig = auth.encode('utf8').rsplit(b'.', 1)
+    sig = b64urldecode(asig)
+    if len(sig) != 64:
+        raise InvalidSignature()
+
+    encoded = utils.encode_dss_signature(
+        s=int(binascii.hexlify(sig[32:]), 16),
+        r=int(binascii.hexlify(sig[:32]), 16)
+    )
+    return payload, encoded
+
+
+def decode(token, key):
+    """Decode a web token into an assertion dictionary
+
+    :param token: VAPID auth token
+    :type token: str
+    :param key: bitarray containing the public key
+    :type key: str
+
+    :return dict of the VAPID claims
+
+    :raise InvalidSignature
+
+    """
+    try:
+        sig_material, signature = extract_signature(token)
+        dkey = b64urldecode(key.encode('utf8'))
+        pkey = ec.EllipticCurvePublicKey.from_encoded_point(
+            ec.SECP256R1(),
+            dkey,
+        )
+        pkey.verify(
+            signature,
+            sig_material,
+            ec.ECDSA(hashes.SHA256())
+        )
+        return json.loads(
+            b64urldecode(sig_material.split(b'.')[1]).decode('utf8')
+        )
+    except InvalidSignature:
+        raise
+    except(ValueError, TypeError, binascii.Error):
+        raise InvalidSignature()
+
+
+def sign(claims, key):
+    """Sign the claims
+
+    :param claims: list of JWS claims
+    :type claims: dict
+    :param key: Private key for signing
+    :type key: ec.EllipticCurvePrivateKey
+    :param algorithm: JWT "alg" descriptor
+    :type algorithm: str
+
+    """
+    header = b64urlencode(b"""{"typ":"JWT","alg":"ES256"}""")
+    # Unfortunately, chrome seems to require the claims to be sorted.
+    claims = b64urlencode(json.dumps(claims,
+                                     separators=(',', ':'),
+                                     sort_keys=True).encode('utf8'))
+    token = "{}.{}".format(header, claims)
+    rsig = key.sign(token.encode('utf8'), ec.ECDSA(hashes.SHA256()))
+    (r, s) = utils.decode_dss_signature(rsig)
+    sig = b64urlencode(num_to_bytes(r, 32) + num_to_bytes(s, 32))
+    return "{}.{}".format(token, sig)