Implement a basic test suite for jwtutil and add extra checks to the decode method

util/security/jwtutil.py

@@ -5,7 +5,8 @@ from datetime import datetime, timedelta
 from jwt import PyJWT
 from jwt.exceptions import (
   InvalidTokenError, DecodeError, InvalidAudienceError, ExpiredSignatureError,
-  ImmatureSignatureError, InvalidIssuedAtError, InvalidIssuerError, MissingRequiredClaimError
+  ImmatureSignatureError, InvalidIssuedAtError, InvalidIssuerError, MissingRequiredClaimError,
+  InvalidAlgorithmError
 )
 
 from cryptography.hazmat.backends import default_backend
@@ -17,14 +18,19 @@ from jwkest.jwk import keyrep, RSAKey, ECKey
 # TOKEN_REGEX defines a regular expression for matching JWT bearer tokens.
 TOKEN_REGEX = re.compile(r'\ABearer (([a-zA-Z0-9+\-_/]+\.)+[a-zA-Z0-9+\-_/]+)\Z')
 
+# ALGORITHM_WHITELIST defines a whitelist of allowed algorithms to be used in JWTs. DO NOT ADD
+# `none` here!
+ALGORITHM_WHITELIST = [
+  'rs256'
+]
 
-class StrictJWT(PyJWT):
-  """ StrictJWT defines a JWT decoder with extra checks. """
+class _StrictJWT(PyJWT):
+  """ _StrictJWT defines a JWT decoder with extra checks. """
 
   @staticmethod
   def _get_default_options():
     # Weird syntax to call super on a staticmethod
-    defaults = super(StrictJWT, StrictJWT)._get_default_options()
+    defaults = super(_StrictJWT, _StrictJWT)._get_default_options()
     defaults.update({
       'require_exp': True,
       'require_iat': True,
@@ -41,14 +47,14 @@ class StrictJWT(PyJWT):
       options['verify_exp'] = True
 
     # Do all of the other checks
-    super(StrictJWT, self)._validate_claims(payload, options, audience, issuer, leeway, **kwargs)
+    super(_StrictJWT, self)._validate_claims(payload, options, audience, issuer, leeway, **kwargs)
 
     now = timegm(datetime.utcnow().utctimetuple())
     self._reject_future_iat(payload, now, leeway)
 
     if 'exp' in payload and options.get('exp_max_s') is not None:
       # Validate that the expiration was not more than exp_max_s seconds after the issue time
-      # or in the absense of an issue time, more than exp_max_s in the future from now
+      # or in the absence of an issue time, more than exp_max_s in the future from now
 
       # This will work because the parent method already checked the type of exp
       expiration = datetime.utcfromtimestamp(int(payload['exp']))
@@ -73,15 +79,30 @@ class StrictJWT(PyJWT):
                                  ' the future.')
 
 
+def decode(jwt, key='', verify=True, algorithms=None, options=None,
+           **kwargs):
+  """ Decodes a JWT. """
+  if not algorithms:
+    raise InvalidAlgorithmError('algorithms must be specified')
+
+  normalized = set([a.lower() for a in algorithms])
+  if 'none' in normalized:
+    raise InvalidAlgorithmError('`none` algorithm is not allowed')
+
+  if set(normalized).intersection(set(ALGORITHM_WHITELIST)) != set(normalized):
+    raise InvalidAlgorithmError('Algorithms `%s` are not whitelisted. Allowed: %s' %
+                                (algorithms, ALGORITHM_WHITELIST))
+
+  return _StrictJWT().decode(jwt, key, verify, algorithms, options, **kwargs)
+
+
 def exp_max_s_option(max_exp_s):
+  """ Returns an options dictionary that sets the maximum expiration seconds for a JWT. """
   return {
     'exp_max_s': max_exp_s,
   }
 
 
-decode = StrictJWT().decode
-
-
 def jwk_dict_to_public_key(jwk):
   """ Converts the specified JWK into a public key. """
   jwkest_key = keyrep(jwk)