Catch TokenAlgorithmError

Instead of letting it go uncaught and causing an error, we now show the
user an appropriate error message.

app/authentication/auth.py

@@ -1,6 +1,8 @@
 from flask import request, _request_ctx_stack, current_app, g
 from notifications_python_client.authentication import decode_jwt_token, get_token_issuer
-from notifications_python_client.errors import TokenDecodeError, TokenExpiredError, TokenIssuerError
+from notifications_python_client.errors import (
+    TokenDecodeError, TokenExpiredError, TokenIssuerError, TokenAlgorithmError
+)
 from notifications_utils import request_helper
 from sqlalchemy.exc import DataError
 from sqlalchemy.orm.exc import NoResultFound
@@ -83,13 +85,14 @@ def requires_auth():
     for api_key in service.api_keys:
         try:
             decode_jwt_token(auth_token, api_key.secret)
+        except TokenExpiredError:
+            err_msg = "Error: Your system clock must be accurate to within 30 seconds"
+            raise AuthError(err_msg, 403, service_id=service.id, api_key_id=api_key.id)
+        except TokenAlgorithmError:
+            err_msg = "Invalid token: algorithm used is not HS256"
+            raise AuthError(err_msg, 403, service_id=service.id, api_key_id=api_key.id)
         except TokenDecodeError:
             continue
-        except TokenExpiredError:
-            err_msg = (
-                "Error: Your system clock must be accurate to within 30 seconds"
-            )
-            raise AuthError(err_msg, 403, service_id=service.id, api_key_id=api_key.id)
 
         if api_key.expiry_date:
             raise AuthError("Invalid token: API key revoked", 403, service_id=service.id, api_key_id=api_key.id)

requirements-app.txt

@@ -20,7 +20,7 @@ psycopg2-binary==2.8.4
 PyJWT==1.7.1
 SQLAlchemy==1.3.10
 
-notifications-python-client==5.4.0
+notifications-python-client==5.4.1
 
 # PaaS
 awscli-cwlogs>=1.4,<1.5

requirements.txt

@@ -22,7 +22,7 @@ psycopg2-binary==2.8.4
 PyJWT==1.7.1
 SQLAlchemy==1.3.10
 
-notifications-python-client==5.4.0
+notifications-python-client==5.4.1
 
 # PaaS
 awscli-cwlogs>=1.4,<1.5
@@ -40,12 +40,12 @@ alembic==1.3.1
 amqp==1.4.9
 anyjson==0.3.3
 attrs==19.3.0
-awscli==1.16.298
+awscli==1.16.301
 bcrypt==3.1.7
 billiard==3.3.0.23
 bleach==3.1.0
 boto3==1.9.221
-botocore==1.13.34
+botocore==1.13.37
 certifi==2019.11.28
 chardet==3.0.4
 Click==7.0
@@ -56,7 +56,7 @@ flask-redis==0.4.0
 future==0.18.2
 greenlet==0.4.15
 idna==2.8
-importlib-metadata==1.2.0
+importlib-metadata==1.3.0
 Jinja2==2.10.3
 jmespath==0.9.4
 kombu==3.0.37

tests/app/authentication/test_authentication.py

@@ -83,6 +83,27 @@ def test_auth_should_not_allow_request_with_no_iat(client, sample_api_key):
     assert exc.value.short_message == 'Invalid token: signature, api token not found'
 
 
+def test_auth_should_not_allow_request_with_non_hs256_algorithm(client, sample_api_key):
+    iss = str(sample_api_key.service_id)
+    # code copied from notifications_python_client.authentication.py::create_jwt_token
+    headers = {
+        "typ": 'JWT',
+        "alg": 'HS512'
+    }
+
+    claims = {
+        'iss': iss,
+        'iat': int(time.time())
+    }
+
+    token = jwt.encode(payload=claims, key=str(uuid.uuid4()), headers=headers).decode()
+
+    request.headers = {'Authorization': 'Bearer {}'.format(token)}
+    with pytest.raises(AuthError) as exc:
+        requires_auth()
+    assert exc.value.short_message == 'Invalid token: algorithm used is not HS256'
+
+
 def test_admin_auth_should_not_allow_request_with_no_iat(client, sample_api_key):
     iss = current_app.config['ADMIN_CLIENT_USER_NAME']