fix: list the supported methods in 405 answers

Author: azmeuk

scim2_server/provider.py

@@ -36,6 +36,7 @@
 from werkzeug.datastructures import ETags
 from werkzeug.exceptions import Forbidden
 from werkzeug.exceptions import HTTPException
+from werkzeug.exceptions import MethodNotAllowed
 from werkzeug.exceptions import NotFound
 from werkzeug.exceptions import NotImplemented as WerkzeugNotImplemented
 from werkzeug.exceptions import PreconditionFailed
@@ -828,7 +829,11 @@ def wsgi_app(self, request: Request, environ: "WSGIEnvironment") -> Response:
             self.log.exception(e)
             return e.get_response(environ)
         except Exception as e:
-            return self.make_error(self.error_from(e))
+            response = self.make_error(self.error_from(e))
+            if isinstance(e, MethodNotAllowed) and e.valid_methods:
+                # RFC 9110 §15.5.6: a 405 answer lists the supported methods.
+                response.headers["Allow"] = ", ".join(sorted(e.valid_methods))
+            return response
 
     def __call__(
         self, environ: "WSGIEnvironment", start_response: "StartResponse"

tests/test_provider.py

@@ -112,6 +112,21 @@ def test_unsupported_method_on_a_reserved_endpoint(self, wsgi, method, path):
 
         assert r.status_code == 405
 
+    @pytest.mark.parametrize(
+        ("method", "path", "allowed"),
+        [
+            ("POST", "/v2/Schemas", "GET, HEAD"),
+            ("GET", "/v2/Bulk", "POST"),
+        ],
+    )
+    def test_method_not_allowed_lists_the_supported_methods(
+        self, wsgi, method, path, allowed
+    ):
+        """A 405 answer tells the methods the endpoint supports."""
+        r = wsgi.request(method, path)
+
+        assert r.headers["Allow"] == allowed
+
     def test_unknown_resource_endpoint(self, wsgi):
         """An endpoint that is neither reserved nor served answers 404."""
         r = wsgi.get("/v2/SchemasArchive")