String+query-extractor.swift

extension String {
    func queryParameter(_ parameter: String) -> String? {
        var fields = [String: String]()
        params.components(separatedBy: "&").forEach {
            let field = $0.components(separatedBy: "=")
            fields[String(field.first ?? "")] = String(field.last ?? "")
        }
        return fields[parameter]
    }
}

// use
let val = params.queryParameter("teste")