feat: Adds CORS Support

[bosvos]

Refs: ASG-5216

[LeonLeibbrandt]

LGTM, very cool.

[LeonLeibbrandt]

go run test/servefile.go

Also when hitting this url for the first time it gives you a full listing of the repo. The correct url is http://localhost:8085/test/cors_test.html

[FritzOnFire]

A whole bunch of small changes, but it should be good to merge after them.

[FritzOnFire]

This feels like fluff, but please move this file one level deeper in case we need to use this folder for other more involved testing setups

New Dir: test/cors.

But then we can probably rename the file to test.html, as it would be obvious what the file is used for.

[FritzOnFire]

Same fluff comment as on the other file

[FritzOnFire]

Suggested change

	### cors_test_server.go
	### serverfile.go

[FritzOnFire]

Suggested change

	A minimal Go HTTP server that serves the `cors_test.html` file on `http://localhost:8080`. This allows you to easily load the test page in your browser.
	A minimal Go HTTP server that serves the `test.html` file on `http://localhost:8080`. This allows you to easily load the test page in your browser.

[FritzOnFire]

Suggested change

	### cors_test.html
	### test.html

[FritzOnFire]

Just to minimize the impact on our standard config.

Suggested change

	// Set the Access-Control-Allow-Origin header, based on allow-list
	s.errorLog.Infof("Forwarding from \"%v\"", req.Header.Get("Origin"))
	_, ok := s.configHttp.Origins[req.Header.Get("Origin")]
	if ok {
	w.Header().Set("Access-Control-Allow-Origin", req.Header.Get("Origin"))
	w.Header().Set("Access-Control-Allow-Credentials", "true")
	// Handle preflight OPTIONS requests
	if req.Method == "OPTIONS" {
	w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
	w.WriteHeader(http.StatusOK)
	return
	}
	}
	if len(s.configHttp.Origins) > 0 {
	// Set the Access-Control-Allow-Origin header, based on allow-list
	og := req.Header.Get("Origin")
	s.errorLog.Infof("Forwarding from \"%v\"", og)
	if _, ok := s.configHttp.Origins[og]; ok {
	w.Header().Set("Access-Control-Allow-Origin", og)
	w.Header().Set("Access-Control-Allow-Credentials", "true")
	// Handle preflight OPTIONS requests
	if req.Method == "OPTIONS" {
	w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
	w.WriteHeader(http.StatusOK)
	return
	}
	}
	}

[bosvos]

I've made the other changes apart from the pointer one. @FritzOnFire

[FritzOnFire]

Just that extra if statement in server.go but then this is good to merge