Regarding the first part, it's easier than you might think to have a false sense of security. I've seen a web application that did, in fact, check the Content-

Regarding the first part, it's easier than you might think to have a false sense of security. I've seen a web application that did, in fact, check the Content-Type header to make sure that "application/json" was there - but it didn't check that the header value started with that. That meant that setting the header to "multipart/form-data; boundary=application/json" was enough to bypass a CORS preflight!