[#158] Support cors

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

cmd/http-gw/settings.go

@@ -56,6 +56,8 @@ const (
 
 	defaultReconnectInterval = time.Minute
 
+	defaultCORSMaxAge = 600 // seconds
+
 	cfgServer      = "server"
 	cfgTLSEnabled  = "tls.enabled"
 	cfgTLSCertFile = "tls.cert_file"
@@ -141,6 +143,14 @@ const (
 	cfgResolveNamespaceHeader   = "resolve_bucket.namespace_header"
 	cfgResolveDefaultNamespaces = "resolve_bucket.default_namespaces"
 
+	// CORS.
+	cfgCORSAllowOrigin      = "cors.allow_origin"
+	cfgCORSAllowMethods     = "cors.allow_methods"
+	cfgCORSAllowHeaders     = "cors.allow_headers"
+	cfgCORSExposeHeaders    = "cors.expose_headers"
+	cfgCORSAllowCredentials = "cors.allow_credentials"
+	cfgCORSMaxAge           = "cors.max_age"
+
 	// Command line args.
 	cmdHelp          = "help"
 	cmdVersion       = "version"
@@ -537,6 +547,15 @@ func fetchDefaultNamespaces(v *viper.Viper) []string {
 	return namespaces
 }
 
+func fetchCORSMaxAge(v *viper.Viper) int {
+	maxAge := v.GetInt(cfgCORSMaxAge)
+	if maxAge <= 0 {
+		maxAge = defaultCORSMaxAge
+	}
+
+	return maxAge
+}
+
 func fetchServers(v *viper.Viper, log *zap.Logger) []ServerInfo {
 	var servers []ServerInfo
 	seen := make(map[string]struct{})