feat: Adds support for multiple decode algorithms

docs/options.rst

@@ -31,6 +31,8 @@ General Options:
                                   Can be set to ``False`` to disable expiration.
 ``JWT_ALGORITHM``                 Which algorithm to sign the JWT with. `See here <https://pyjwt.readthedocs.io/en/latest/algorithms.html>`_
                                   for the options. Defaults to ``'HS256'``.
+``JWT_DECODE_ALGORITHMS``         Which algorithms are allowed to decode a JWT.
+                                  Defaults to a list with only the algorithm set in ``JWT_ALGORITHM``.
 ``JWT_SECRET_KEY``                The secret key needed for symmetric based signing algorithms,
                                   such as ``HS*``. If this is not set, we use the
                                   flask ``SECRET_KEY`` value instead.

flask_jwt_extended/config.py

@@ -218,6 +218,15 @@ def refresh_expires(self):
     def algorithm(self):
         return current_app.config['JWT_ALGORITHM']
 
+    @property
+    def decode_algorithms(self):
+        algorithms = current_app.config['JWT_DECODE_ALGORITHMS']
+        if not algorithms:
+            return [self.algorithm]
+        if self.algorithm not in algorithms:
+            algorithms.append(self.algorithm)
+        return algorithms
+
     @property
     def blacklist_enabled(self):
         return current_app.config['JWT_BLACKLIST_ENABLED']

flask_jwt_extended/jwt_manager.py

@@ -194,6 +194,9 @@ def _set_default_configuration_options(app):
         # https://github.com/jpadilla/pyjwt/blob/master/jwt/api_jwt.py
         app.config.setdefault('JWT_ALGORITHM', 'HS256')
 
+        # What algorithms are allowed to decode a token
+        app.config.setdefault('JWT_DECODE_ALGORITHMS', None)
+
         # Secret key to sign JWTs with. Only used if a symmetric algorithm is
         # used (such as the HS* algorithms). We will use the app secret key
         # if this is not set.

flask_jwt_extended/tokens.py

@@ -112,15 +112,15 @@ def encode_refresh_token(identity, secret, algorithm, expires_delta, user_claims
                        json_encoder=json_encoder)
 
 
-def decode_jwt(encoded_token, secret, algorithm, identity_claim_key,
+def decode_jwt(encoded_token, secret, algorithms, identity_claim_key,
                user_claims_key, csrf_value=None, audience=None,
                leeway=0, allow_expired=False):
     """
     Decodes an encoded JWT
 
     :param encoded_token: The encoded JWT string to decode
     :param secret: Secret key used to encode the JWT
-    :param algorithm: Algorithm used to encode the JWT
+    :param algorithms: Algorithms allowed to decode the token
     :param identity_claim_key: expected key that contains the identity
     :param user_claims_key: expected key that contains the user claims
     :param csrf_value: Expected double submit csrf value
@@ -134,7 +134,7 @@ def decode_jwt(encoded_token, secret, algorithm, identity_claim_key,
         options['verify_exp'] = False
 
     # This call verifies the ext, iat, nbf, and aud claims
-    data = jwt.decode(encoded_token, secret, algorithms=[algorithm], audience=audience,
+    data = jwt.decode(encoded_token, secret, algorithms=algorithms, audience=audience,
                       leeway=leeway, options=options)
 
     # Make sure that any custom claims we expect in the token are present

flask_jwt_extended/utils.py

@@ -78,7 +78,7 @@ def decode_token(encoded_token, csrf_value=None, allow_expired=False):
     """
     jwt_manager = _get_jwt_manager()
     unverified_claims = jwt.decode(
-        encoded_token, verify=False, algorithms=config.algorithm
+        encoded_token, verify=False, algorithms=config.decode_algorithms
     )
     unverified_headers = jwt.get_unverified_header(encoded_token)
     # Attempt to call callback with both claims and headers, but fallback to just claims
@@ -98,7 +98,7 @@ def decode_token(encoded_token, csrf_value=None, allow_expired=False):
         return decode_jwt(
             encoded_token=encoded_token,
             secret=secret,
-            algorithm=config.algorithm,
+            algorithms=config.decode_algorithms,
             identity_claim_key=config.identity_claim_key,
             user_claims_key=config.user_claims_key,
             csrf_value=csrf_value,
@@ -110,7 +110,7 @@ def decode_token(encoded_token, csrf_value=None, allow_expired=False):
         expired_token = decode_jwt(
             encoded_token=encoded_token,
             secret=secret,
-            algorithm=config.algorithm,
+            algorithms=config.decode_algorithms,
             identity_claim_key=config.identity_claim_key,
             user_claims_key=config.user_claims_key,
             csrf_value=csrf_value,

tests/test_config.py

@@ -55,6 +55,7 @@ def test_default_configs(app):
         assert config.access_expires == timedelta(minutes=15)
         assert config.refresh_expires == timedelta(days=30)
         assert config.algorithm == 'HS256'
+        assert config.decode_algorithms == ['HS256']
         assert config.is_asymmetric is False
         assert config.blacklist_enabled is False
         assert config.blacklist_checks == ('access', 'refresh')
@@ -105,6 +106,7 @@ def test_override_configs(app, delta_func):
     app.config['JWT_ACCESS_TOKEN_EXPIRES'] = delta_func(minutes=5)
     app.config['JWT_REFRESH_TOKEN_EXPIRES'] = delta_func(days=5)
     app.config['JWT_ALGORITHM'] = 'HS512'
+    app.config['JWT_DECODE_ALGORITHMS'] = ['HS512', 'HS256']
 
     app.config['JWT_BLACKLIST_ENABLED'] = True
     app.config['JWT_BLACKLIST_TOKEN_CHECKS'] = ('refresh',)
@@ -156,6 +158,7 @@ class CustomJSONEncoder(JSONEncoder):
         assert config.access_expires == delta_func(minutes=5)
         assert config.refresh_expires == delta_func(days=5)
         assert config.algorithm == 'HS512'
+        assert config.decode_algorithms == ['HS512', 'HS256']
 
         assert config.blacklist_enabled is True
         assert config.blacklist_checks == ('refresh',)
@@ -396,3 +399,11 @@ def test_depreciated_options(app):
             assert len(w) == 2
             assert w[0].category == DeprecationWarning
             assert w[1].category == DeprecationWarning
+
+
+def test_missing_algorithm_in_decode_algorithms(app):
+    app.config['JWT_ALGORITHM'] = 'RS256'
+    app.config['JWT_DECODE_ALGORITHMS'] = ['HS512']
+
+    with app.test_request_context():
+        assert config.decode_algorithms == ['HS512', 'RS256']