This it the right way to do client IDs / secrets and local builds

lib/keys.properties.example

@@ -0,0 +1,10 @@
+# OpenStreetMap OAuth Client IDs
+# Copy this file to keys.properties and fill in your values for local development
+# These are used as fallback when environment variables are not provided via --dart-define.
+# 
+# Get your client IDs from:
+# Production: https://www.openstreetmap.org/oauth2/applications
+# Sandbox: https://master.apis.dev.openstreetmap.org/oauth2/applications
+
+OSM_PROD_CLIENTID=your_production_client_id_here
+OSM_SANDBOX_CLIENTID=your_sandbox_client_id_here