Just recently in the salesforce sandbox environment, in the REST API login JSON response a new field "is_readonly" is returned that causes our 3rd party code (we are using the Apache Camel Salesforce component) to fail.

The official documentation doesn't mention this "is_readonly" field:
https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_understanding_web_server_oauth_flow.htm