Properly handle protected endpoints with query strings.

To facilitate nginx configuration, we've changed the redirect from
https://$http_host/saml/login?url=$request_uri to
https://$http_host/saml/login$request_uri. I erroneously thought $request_uri
would be encoded, but it wasn't. The old way created a potentially invalid uri.
The new way preserves the original url that we want to come back to.

Author: jeffFranklin

README.md

@@ -7,9 +7,10 @@ URL, the proxy will take care of the rest.
 Example nginx.conf would look like the following...
 
 ```
-location /secure {
-    auth_request /saml/status/group/uw_example_group;
+location / {
+    auth_request /saml/status/group/uw_it_all;
     auth_request_set $auth_user $upstream_http_x_saml_user;
+    error_page 401 = @login_required;
     proxy_set_header Remote-User $auth_user;
     proxy_pass http://secure:5000/;
 }
@@ -18,21 +19,23 @@ location /saml/ {
     proxy_set_header Host $http_host;
     proxy_set_header X-Forwarded-Proto $scheme;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-    proxy_set_header X-Forwarded-Prefix /saml;
     proxy_set_header X-Saml-Entity-Id https://samldemo.iamdev.s.uw.edu/saml;
+    # acs - post-back url registered with the IdP.
     proxy_set_header X-Saml-Acs /saml/login;
     proxy_pass http://saml:5000/;
 }
 
-location @error401 {
-    return 302 https://$http_host/saml/login?url=$request_uri;
+location @login_required {
+    return 302 https://$http_host/saml/login$request_uri;
 }
 ```
 
+See the [example nginx config](test/nginx/server.conf) for more examples.
+
 ## SECRET_KEY
 
 This app wants an environment variable `SECRET_KEY`, which should be a secure,
 randomly-generated string. Otherwise, we generate one on the fly, which only
-works long as the app is running, and won't work in a distributed environment.
+works as long as the app is running, and won't work in a distributed environment.
 SECRET_KEY is used to sign cookies, so setting a new key effectively
 invalidates all existing sessions.

app.py

@@ -29,35 +29,58 @@ def status(group=None):
     403 if a group was requested that the user is not a member of, or 200
     if the user is authenticated.
 
-        group - a UW Group the user must be a member of.
+    group - a UW Group the user must be a member of. An SP must be registered
+        to receive that group.
     """
     userid = session.get('userid')
     groups = session.get('groups', [])
     if not userid:
         abort(401)
     if group and group not in groups:
+        message = f"{userid} not a member of {group} or SP can't receive it"
+        app.logger.error(message)
         abort(403)
     headers = {'X-Saml-User': userid,
                'X-Saml-Groups': ':'.join(groups)}
     txt = f'Logged in as: {userid}\nGroups: {str(groups)}'
     return Response(txt, status=200, headers=headers)
 
 
+def _saml_args():
+    """Get entity_id and acs_url from request.headers."""
+    return {
+        'entity_id': request.headers['X-Saml-Entity-Id'],
+        'acs_url': urljoin(request.url_root, request.headers['X-Saml-Acs'])
+    }
+
+
+@app.route('/login/')
+@app.route('/login/<path:return_to>')
+def login_redirect(return_to=''):
+    """
+    Redirect to the IdP for SAML initiation.
+    
+    return_to - the path to redirect back to after authentication. This and
+        the request.query_string are set on the SAML RelayState.
+    """
+    query_string = '?' + request.query_string.decode()
+    if query_string == '?':
+        query_string = ''
+    return_to = f'/{return_to}{query_string}'
+    args = _saml_args()
+    return redirect(uw_saml2.login_redirect(return_to=return_to, **args))
+
+
 @app.route('/login', methods=['GET', 'POST'])
 def login():
     """
-    Return a SAML Request redirect, or process a SAML Response, depending
-    on whether GET or POST.
+    Process a SAML Response, and set the uwnetid and groups on the session.
     """
     session.clear()
-    args = {
-        'entity_id': request.headers['X-Saml-Entity-Id'],
-        'acs_url': urljoin(request.url_root, request.headers['X-Saml-Acs'])
-    }
     if request.method == 'GET':
-        args['return_to'] = request.args.get('url', None)
-        return redirect(uw_saml2.login_redirect(**args))
+        return login_redirect()
 
+    args = _saml_args()
     attributes = uw_saml2.process_response(request.form, **args)
 
     session['userid'] = attributes['uwnetid']
@@ -80,5 +103,7 @@ def logout():
 def healthz():
     """Return a 200 along with some useful links."""
     return '''
-    <p><a href="login">Sign in</a></p><p><a href="logout">Logout</a></p>
+    <p><a href="login">Sign in</a></p>
+    <p><a href="status">Status</a></p>
+    <p><a href="logout">Logout</a></p>
     '''

docker-compose.yml

@@ -0,0 +1,13 @@
+version: '3'
+services:
+  saml:
+    build: .
+    image: nginx-saml-proxy
+    volumes:
+      - ./app.py:/app/app.py
+  nginx:
+    build: test/nginx
+    image: mynginx
+    ports: ["443:443"]
+    volumes:
+      - ./test/nginx/server.conf:/etc/nginx/conf.d/server.conf

test/nginx/Dockerfile

@@ -0,0 +1,17 @@
+FROM nginx as certbuilder
+
+RUN apt-get update && apt-get install -y ssl-cert && apt-get clean
+RUN mkdir /ssl && \
+    cp -p /etc/ssl/private/ssl-cert-snakeoil.key /ssl/key.pem && \
+    cp -p /etc/ssl/certs/ssl-cert-snakeoil.pem /ssl/cert.pem
+
+FROM nginx
+
+EXPOSE 80
+EXPOSE 443
+
+RUN rm /etc/nginx/conf.d/* && mkdir /static
+COPY server.conf /etc/nginx/conf.d/server.conf
+COPY --from=certbuilder /ssl /etc/nginx/ssl
+
+CMD ["nginx", "-g", "daemon off;"]

test/nginx/server.conf

@@ -0,0 +1,33 @@
+server {
+  listen 443 ssl;
+  ssl_certificate /etc/nginx/ssl/cert.pem;
+  ssl_certificate_key /etc/nginx/ssl/key.pem;
+  root /usr/share/nginx/html;
+
+  # anyone with a UW NetID can access this
+  location / {
+    auth_request /saml/status;
+    auth_request_set $auth_user $upstream_http_x_saml_user;
+    error_page 401 = @login_required;
+  }
+
+  # user must be a member of uw_it_all
+  location /secure {
+      auth_request /saml/status/group/uw_it_all;
+      error_page 401 = @login_required;
+      alias /usr/share/nginx/html;
+  }
+
+  location /saml/ {
+    proxy_set_header Host $http_host;
+    proxy_set_header X-Forwarded-Proto $scheme;
+    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    proxy_set_header X-Saml-Entity-Id https://samldemo.iamdev.s.uw.edu/saml;
+    proxy_set_header X-Saml-Acs /saml/login;
+    proxy_pass http://saml:5000/;
+  }
+
+  location @login_required {
+    return 302 https://$http_host/saml/login$request_uri;
+  }
+}