add options feature on apps package and add a SetHost option to force host on multiple subdomains that should mean the same exact application, so any handler should run based on the same Host field

apps/switch_options_test.go

@@ -0,0 +1,38 @@
+package apps
+
+import (
+	"testing"
+
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/httptest"
+)
+
+func TestSetHost(t *testing.T) {
+	var (
+		index = func(ctx iris.Context) {
+			ctx.Header("Server", ctx.Application().String())
+			ctx.WriteString(ctx.Host())
+		}
+
+		forceHost = "www.mydomain.com"
+	)
+
+	rootApp := iris.New().SetName("My Server")
+	rootApp.Get("/", index)
+
+	switcher := Switch(Hosts{
+		{"^(www.)?mydomain.com$", rootApp},
+	}, SetHost(forceHost))
+
+	e := httptest.New(t, switcher)
+	tests := []*httptest.Request{
+		e.GET("/").WithURL("http://mydomain.com"),
+		e.GET("/").WithURL("http://www.mydomain.com"),
+	}
+
+	for _, tt := range tests {
+		ex := tt.Expect().Status(iris.StatusOK)
+		ex.Header("Server").Equal(rootApp.String())
+		ex.Body().Equal(forceHost)
+	}
+}