关于WKWebView cookie的问题很多人都遇到过，网上资料也比较多，代码参差不齐，此代码经测试可行：

/* 处理cookie问题 */
    func webView(_ webView: WKWebView, decidePolicyFor navigationResponse: WKNavigationResponse, decisionHandler: @escaping (WKNavigationResponsePolicy) -> Void) {
        if #available(iOS 12.0, *) {
            let cookieStore: WKHTTPCookieStore = webView.configuration.websiteDataStore.httpCookieStore
            cookieStore.getAllCookies({ cookies in
                self.setCookie(cookies)
            })
        } else {
            let response = navigationResponse.response as? HTTPURLResponse
            var cookies: [HTTPCookie]? = nil
            if let all = response?.allHeaderFields as? [String : String], let URL = response?.url {
                cookies = HTTPCookie.cookies(withResponseHeaderFields: all, for: URL)
            }
            self.setCookie(cookies)
        }
        decisionHandler(WKNavigationResponsePolicy.allow)
    }
    
    func setCookie(_ cookies: [Any]?) {
        for cookie in cookies as? [HTTPCookie] ?? [] {
            let httpCookie: HTTPCookie? = fixExpiresDate(with: cookie)
            if let httpCookie = httpCookie {
                HTTPCookieStorage.shared.setCookie(httpCookie)
            }
        }
    }
    
    func fixExpiresDate(with cookie: HTTPCookie?) -> HTTPCookie? {
        var propertiesDic = cookie?.properties
        if propertiesDic?[HTTPCookiePropertyKey.expires] == nil {
            propertiesDic?[HTTPCookiePropertyKey.expires] = Date(timeIntervalSinceNow: 60 * 60 * 24 * 7)
            propertiesDic?[HTTPCookiePropertyKey.discard] = 0
        }
        var newCookie: HTTPCookie? = nil
        if let propertiesDic = propertiesDic {
            newCookie = HTTPCookie(properties: propertiesDic)
        }
        return newCookie
    }