🔒️(backend) secure native app OIDC login with exchange codes

Add one-time exchange code mechanism for native app OIDC login.
Instead of exposing session ID in redirect URL, generates a
short-lived single-use code stored in Redis. Native apps exchange
this code for the session ID via a dedicated API endpoint.

Includes NativeAppRedirect for custom URL schemes, rate limiting,
logging, and whitelist of allowed schemes.

Closes #1153

Co-Authored-By: gigi206

src/backend/core/authentication/views.py

@@ -0,0 +1,103 @@
+"""Custom OIDC authentication views for native app support.
+
+When a native app (iOS, Android, Desktop) initiates OIDC login, it sets
+`returnTo` to a custom URL scheme (e.g. `visio://auth-callback`). After
+the OIDC flow completes, Django sets the session cookie and redirects to
+that URL. However, native apps cannot read browser cookies — they need
+the session ID passed explicitly.
+
+Instead of exposing the session ID directly in the redirect URL, this
+module generates a short-lived, single-use exchange code. The native app
+then exchanges this code for the session ID via a dedicated API endpoint.
+"""
+
+import uuid
+from urllib.parse import urlencode, urlparse
+
+from django.conf import settings
+from django.core.cache import cache
+from django.http import HttpResponseRedirect
+
+from lasuite.oidc_login.views import (
+    OIDCAuthenticationCallbackView as BaseCallbackView,
+    OIDCAuthenticationRequestView as BaseRequestView,
+)
+
+# Cache key prefix and TTL for exchange codes
+EXCHANGE_CODE_PREFIX = "auth_exchange:"
+EXCHANGE_CODE_TTL = 30  # seconds
+
+
+class NativeAppRedirect(HttpResponseRedirect):
+    """HttpResponseRedirect subclass that allows native app custom URL schemes.
+
+    Django's HttpResponseRedirect only allows http, https, and ftp schemes.
+    Native apps use custom schemes (e.g. visio://) for deep links, which
+    Django rejects with DisallowedRedirect. This subclass extends
+    allowed_schemes with the configured native app schemes.
+    """
+
+    allowed_schemes = HttpResponseRedirect.allowed_schemes + list(
+        getattr(settings, "NATIVE_APP_REDIRECT_SCHEMES", [])
+    )
+
+
+class OIDCAuthenticationRequestView(BaseRequestView):
+    """Custom authenticate view that preserves native app returnTo in session.
+
+    mozilla-django-oidc's get_next_url() rejects custom URL schemes
+    (e.g. visio://auth-callback) because url_has_allowed_host_and_scheme()
+    only allows http/https. We intercept the returnTo parameter and store
+    it directly in the session for whitelisted schemes, bypassing the
+    safety check (which is not relevant for native app deep links).
+    """
+
+    def get(self, request):
+        redirect_field = getattr(settings, "OIDC_REDIRECT_FIELD_NAME", "returnTo")
+        return_to = request.GET.get(redirect_field, "")
+        parsed = urlparse(return_to)
+        allowed_schemes = getattr(settings, "NATIVE_APP_REDIRECT_SCHEMES", [])
+
+        response = super().get(request)
+
+        # Override oidc_login_next AFTER super() which set it to None
+        # via get_next_url() rejecting the custom scheme.
+        if parsed.scheme in allowed_schemes:
+            request.session["oidc_login_next"] = return_to
+            request.session.save()
+
+        return response
+
+
+class OIDCAuthenticationCallbackView(BaseCallbackView):
+    """Callback view that generates an exchange code for native app deep links."""
+
+    def login_success(self):
+        """After successful login, append exchange code for whitelisted scheme redirects."""
+        # Temporarily remove native redirect from session to prevent
+        # super().login_success() from raising DisallowedRedirect when
+        # it tries HttpResponseRedirect with a custom scheme.
+        native_redirect = self.request.session.pop("oidc_login_next", None)
+        allowed_schemes = getattr(settings, "NATIVE_APP_REDIRECT_SCHEMES", [])
+        parsed = urlparse(native_redirect or "")
+
+        if native_redirect and parsed.scheme in allowed_schemes:
+            # Let super() redirect to the default URL (homepage)
+            super().login_success()
+
+            # Generate a short-lived, single-use exchange code
+            exchange_code = uuid.uuid4().hex
+            session_key = self.request.session.session_key
+            cache.set(
+                f"{EXCHANGE_CODE_PREFIX}{exchange_code}",
+                session_key,
+                EXCHANGE_CODE_TTL,
+            )
+
+            separator = "&" if parsed.query else "?"
+            new_url = (
+                f"{native_redirect}{separator}{urlencode({'code': exchange_code})}"
+            )
+            return NativeAppRedirect(new_url)
+
+        return super().login_success()