fix: only customize swagger UI if we have init oauth

Author: alukach

src/stac_auth_proxy/app.py

@@ -80,14 +80,20 @@ async def lifespan(app: FastAPI):
     # Handlers (place catch-all proxy handler last)
     #
 
-    if settings.swagger_ui_endpoint:
-        assert (
-            settings.openapi_spec_endpoint
-        ), "openapi_spec_endpoint must be set when using swagger_ui_endpoint"
+    # If we have customized Swagger UI Init settings (e.g. a provided client_id)
+    # then we need to serve our own Swagger UI in place of the upstream's. This requires
+    # that we know the Swagger UI endpoint and the OpenAPI spec endpoint.
+    if all(
+        [
+            settings.swagger_ui_endpoint,
+            settings.openapi_spec_endpoint,
+            settings.swagger_ui_init_oauth,
+        ]
+    ):
         app.add_route(
             settings.swagger_ui_endpoint,
             SwaggerUI(
-                openapi_url=settings.openapi_spec_endpoint,
+                openapi_url=settings.openapi_spec_endpoint,  # type: ignore
                 init_oauth=settings.swagger_ui_init_oauth,
             ).route,
             include_in_schema=False,