fix CORS for flutter web
fix CORS for flutter web

With this change appOrigin doesn't do an exact match, instead it returns the client's origin header if it starts with any of the appOrigins. i.s. A source port in the url string does not interfere with matching. The Origin header cannot be set in a chrome-js XmlHttpRequest. It always sends "http://localhost:<port>" and the source port varies.  Other targets can set Origin header directly.  This if you think web could be useful for mobile app development.

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