Parse the claims string in JWT

So far the unverified claims of JWSs were parsed. While the claims in a
JWT need to be a dict of fields, RFC7520 indicates that the claims in a
JWS don't have to be.

Therefore this commit parses only JWT claims into dicts.

Author: 0x64746b

jose/jws.py

@@ -124,11 +124,7 @@ def get_unverified_claims(token):
         JWSError: If there is an exception decoding the token.
     """
     header, claims, signing_input, signature = _load(token)
-
-    try:
-        return json.loads(claims.decode('utf-8'))
-    except ValueError as e:
-        raise JWSError('Invalid claims string: %s' % e)
+    return claims
 
 
 def _encode_header(algorithm, additional_headers=None):

jose/jwt.py

@@ -184,7 +184,10 @@ def get_unverified_claims(token):
     except:
         raise JWTError('Error decoding token claims.')
 
-    return claims
+    try:
+        return json.loads(claims.decode('utf-8'))
+    except ValueError as e:
+        raise JWTError('Invalid claims string: %s' % e)
 
 
 def _validate_iat(claims):