Feat: implement OAuth/OIDC sign on with Authlib

.devcontainer/.env.sample

@@ -34,5 +34,10 @@ DJANGO_RATE_LIMIT=0
 DJANGO_RATE_LIMIT_METHODS=GET,POST,PUT,DELETE
 DJANGO_RATE_LIMIT_PERIOD=0
 
+DJANGO_OAUTH_AUTHORITY=https://example.com
+DJANGO_OAUTH_CLIENT_ID=client-id-123
+DJANGO_OAUTH_CLIENT_NAME=client_name
+DJANGO_OAUTH_SCOPE=scope
+
 # tests config
 CYPRESS_baseUrl=http://client:8000

benefits/core/__init__.py

@@ -8,6 +8,3 @@ class CoreAppConfig(AppConfig):
     name = "benefits.core"
     label = "core"
     verbose_name = "Core"
-
-
-default_app_config = "benefits.core.CoreAppConfig"

benefits/core/migrations/0001_initial.py

@@ -29,17 +29,6 @@ class Migration(migrations.Migration):
             name="AuthProvider",
             fields=[
                 ("id", models.AutoField(primary_key=True, serialize=False)),
-                ("authority", models.TextField(help_text="Authorization server address")),
-                ("client_id", models.TextField(help_text="The application ID registered with auth server")),
-                ("redirect_uri", models.TextField(help_text="Post-login, the user is redirected here")),
-                ("post_logout_redirect_uri", models.TextField(help_text="Post-logout, the user is redirected here")),
-                ("response_type", models.TextField(help_text='Must be "code" to use the authorization-code flow')),
-                (
-                    "scope",
-                    models.TextField(
-                        help_text='Space-delimited list. If you need refresh tokens, you must add the "offline access" scope'
-                    ),
-                ),
                 ("sign_in_button_label", models.TextField()),
                 ("sign_out_button_label", models.TextField()),
             ],

benefits/core/models.py

@@ -32,17 +32,9 @@ def jwk(self):
 class AuthProvider(models.Model):
     """An entity that provides authentication for eligibility verifiers."""
 
-    # fmt: off
     id = models.AutoField(primary_key=True)
-    authority = models.TextField(help_text="Authorization server address")
-    client_id = models.TextField(help_text="The application ID registered with auth server")
-    redirect_uri = models.TextField(help_text="Post-login, the user is redirected here")
-    post_logout_redirect_uri = models.TextField(help_text="Post-logout, the user is redirected here")
-    response_type = models.TextField(help_text="Must be \"code\" to use the authorization-code flow")
-    scope = models.TextField(help_text="Space-delimited list. If you need refresh tokens, you must add the \"offline access\" scope")  # noqa: 503
     sign_in_button_label = models.TextField()
     sign_out_button_label = models.TextField()
-    # fmt: on
 
 
 class EligibilityType(models.Model):

benefits/eligibility/__init__.py

@@ -8,6 +8,3 @@ class EligibilityAppConfig(AppConfig):
     name = "benefits.eligibility"
     label = "eligibility"
     verbose_name = "Eligibility Verification"
-
-
-default_app_config = "benefits.eligibility.EligibilityAppConfig"

benefits/eligibility/views.py

@@ -11,6 +11,7 @@
 from benefits.core import middleware, recaptcha, session, viewmodels
 from benefits.core.models import EligibilityVerifier
 from benefits.core.views import PageTemplateResponse
+from benefits.settings import OAUTH_CLIENT_NAME
 from . import analytics, api, forms
 
 
@@ -58,12 +59,15 @@ def index(request):
 def start(request):
     """View handler for the eligibility verification getting started screen."""
 
-    session.update(request, eligibility_types=[])
+    session.update(request, eligibility_types=[], origin=reverse("eligibility:start"))
     verifier = session.verifier(request)
 
-    if verifier.requires_authentication:
+    if verifier.requires_authentication and not session.auth(request):
+        if OAUTH_CLIENT_NAME is None:
+            raise Exception("EligibilityVerifier requires authentication, but OAUTH_CLIENT_NAME is None")
+
         auth_provider = verifier.auth_provider
-        button = viewmodels.Button.external(text=_(auth_provider.sign_in_button_label), url="#", id="login")
+        button = viewmodels.Button.external(text=_(auth_provider.sign_in_button_label), url=reverse("oauth:login"), id="login")
     else:
         button = viewmodels.Button.primary(text=_("eligibility.buttons.continue"), url=reverse("eligibility:confirm"))
 

benefits/enrollment/__init__.py

@@ -8,6 +8,3 @@ class EnrollmentAppConfig(AppConfig):
     name = "benefits.enrollment"
     label = "enrollment"
     verbose_name = "Benefits Enrollment"
-
-
-default_app_config = "benefits.enrollment.EnrollmentAppConfig"

benefits/oauth/__init__.py

@@ -0,0 +1,10 @@
+"""
+The oauth application: Implements OAuth-based authentication
+"""
+from django.apps import AppConfig
+
+
+class OAuthAppConfig(AppConfig):
+    name = "benefits.oauth"
+    label = "oauth"
+    verbose_name = "Benefits OAuth"

benefits/oauth/urls.py

@@ -0,0 +1,11 @@
+from django.urls import path
+
+from . import views
+
+
+app_name = "oauth"
+urlpatterns = [
+    # /oauth
+    path("login", views.login, name="login"),
+    path("authorize", views.authorize, name="authorize"),
+]

benefits/oauth/views.py

@@ -0,0 +1,42 @@
+from django.shortcuts import redirect
+from django.urls import reverse
+
+from authlib.integrations.django_client import OAuth
+
+from benefits.core import session
+from benefits.settings import OAUTH_CLIENT_NAME
+
+
+if OAUTH_CLIENT_NAME:
+    _oauth = OAuth()
+    _oauth.register(OAUTH_CLIENT_NAME)
+    oauth_client = _oauth.create_client(OAUTH_CLIENT_NAME)
+
+
+ROUTE_AUTH = "oauth:authorize"
+ROUTE_START = "eligibility:start"
+ROUTE_CONFIRM = "eligibility:confirm"
+
+
+def login(request):
+    if not oauth_client:
+        raise Exception("No OAuth client")
+
+    route = reverse(ROUTE_AUTH)
+    redirect_uri = request.build_absolute_uri(route)
+
+    return oauth_client.authorize_redirect(request, redirect_uri)
+
+
+def authorize(request):
+    if not oauth_client:
+        raise Exception("No OAuth client")
+
+    token = oauth_client.authorize_access_token(request)
+
+    if token is None:
+        return redirect(ROUTE_START)
+    else:
+        # we are intentionally not storing anything about the user, including their token
+        session.update(request, auth=True)
+        return redirect(ROUTE_CONFIRM)

benefits/settings.py

@@ -30,6 +30,7 @@ def _filter_empty(ls):
     "benefits.core",
     "benefits.enrollment",
     "benefits.eligibility",
+    "benefits.oauth",
 ]
 
 if ADMIN:
@@ -70,9 +71,17 @@ def _filter_empty(ls):
 CSRF_COOKIE_HTTPONLY = True
 CSRF_TRUSTED_ORIGINS = _filter_empty(os.environ["DJANGO_TRUSTED_ORIGINS"].split(","))
 
-SESSION_COOKIE_SAMESITE = "Strict"
+# With `Strict`, the user loses their Django session between leaving our app to
+# sign in with OAuth, and coming back into our app from the OAuth redirect.
+# This is because `Strict` disallows our cookie being sent from an external
+# domain and so the session cookie is lost.
+#
+# `Lax` allows the cookie to travel with the user and be sent back to us by the
+# OAuth server, as long as the request is "safe" i.e. GET
+SESSION_COOKIE_SAMESITE = "Lax"
 SESSION_ENGINE = "django.contrib.sessions.backends.signed_cookies"
 SESSION_EXPIRE_AT_BROWSER_CLOSE = True
+SESSION_COOKIE_NAME = "_benefitssessionid"
 
 if not DEBUG:
     CSRF_COOKIE_SECURE = True
@@ -148,6 +157,19 @@ def _filter_empty(ls):
         ]
     )
 
+# OAuth configuration
+
+OAUTH_CLIENT_NAME = os.environ.get("DJANGO_OAUTH_CLIENT_NAME")
+
+if OAUTH_CLIENT_NAME:
+    AUTHLIB_OAUTH_CLIENTS = {
+        OAUTH_CLIENT_NAME: {
+            "client_id": os.environ.get("DJANGO_OAUTH_CLIENT_ID"),
+            "server_metadata_url": f"{os.environ.get('DJANGO_OAUTH_AUTHORITY')}/.well-known/openid-configuration",
+            "client_kwargs": {"code_challenge_method": "S256", "scope": os.environ.get("DJANGO_OAUTH_SCOPE")},
+        }
+    }
+
 # Internationalization
 
 LANGUAGE_CODE = "en"

benefits/urls.py

@@ -8,7 +8,7 @@
 
 from django.urls import include, path
 
-from benefits.settings import ADMIN
+from benefits.settings import ADMIN, OAUTH_CLIENT_NAME
 
 
 logger = logging.getLogger(__name__)
@@ -28,7 +28,13 @@
 if ADMIN:
     from django.contrib import admin
 
-    logger.debug("Register admin/ urls")
+    logger.debug("Register admin urls")
     urlpatterns.append(path("admin/", admin.site.urls))
 else:
     logger.debug("Skip url registrations for admin")
+
+if OAUTH_CLIENT_NAME:
+    logger.info("Register oauth urls")
+    urlpatterns.append(path("oauth/", include("benefits.oauth.urls")))
+else:
+    logger.debug("Skip url registrations for oauth")

fixtures/02_authprovider.json

@@ -3,12 +3,6 @@
       "model": "core.authprovider",
       "pk": 1,
       "fields": {
-        "authority": "https://example.com",
-        "client_id": "b2c086d3-2e78-4e1f-8dde-f4b162743048",
-        "redirect_uri": "https://example.com/redirect",
-        "post_logout_redirect_uri": "https://example.com/logout",
-        "response_type": "code",
-        "scope": "openid",
         "sign_in_button_label": "eligibility.buttons.signin",
         "sign_out_button_label": "eligibility.buttons.signout"
       }

requirements.txt

@@ -1,3 +1,4 @@
+Authlib==1.0.1
 cryptography==36.0.2
 Django==3.2.12
 django-csp==3.7