Browsers like Chrome or Safari include an Origin header for same-origin
POST/PUT/DELETE requests, not only for cross-origin requests.
Before this commit, these same-origin requests would have been detected
as potential cross-origin requests, and rejected if the same-origin domain
is not part of the configured allowedOrigins.
This commit avoid to reject same-origin requests by reusing the logic
introduced in Spring 4.1 for detecting reliably Websocket/SockJS
same-origin requests with the WebUtils.isValidOrigin() method. This
logic has been extracted in a new WebUtils.isSameOrigin() method.
Issue: SPR-13206
84138abfd1