callbacks.go
func Only(ops ...Operation) Matcher {
	return func(ctx *Context) bool {
		// allow if operation is listed
		for _, op := range ops {
			if op == ctx.Operation {
				return true
			}
		}

		return false
	}
}
func Only(ops ...Operation) Matcher {
	return func(ctx *Context) bool {
		// allow if operation is listed
		for _, op := range ops {
			if op == ctx.Operation {
				return true
			}
		}

		return false
	}
}
// Only will match if the operation is present in the provided list.