Catch JWSErrors in jwt.decode()

So far exceptions raised in `jws.verify()` weren't caught in the above
function, which led to it raising (undocumented) exceptions from the
underlying module.

This commit transforms said exceptions. This includes cases of invalid
payload padding, error handling for which had previously been attached
to the `json.loads()` call.

jose/jwt.py

@@ -10,6 +10,7 @@
 
 from jose import jws
 
+from .exceptions import JWSError
 from .exceptions import JWTClaimsError
 from .exceptions import JWTError
 from .exceptions import ExpiredSignatureError
@@ -112,12 +113,14 @@ def decode(token, key, algorithms=None, options=None, audience=None, issuer=None
  defaults.update(options)
 
  verify_signature = defaults.get('verify_signature', True)
- payload = jws.verify(token, key, algorithms, verify=verify_signature)
+
+ try:
+ payload = jws.verify(token, key, algorithms, verify=verify_signature)
+ except JWSError as e:
+ raise JWTError(e)
 
  try:
  claims = json.loads(payload.decode('utf-8'))
- except (TypeError, binascii.Error):
- raise JWTError('Invalid payload padding')
  except ValueError as e:
  raise JWTError('Invalid payload string: %s' % e)