//修改userAgent
+ (void)addToWebViewUserAgent:(NSString *)addAgent
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        WKWebView *webView = [WKWebView new];
        [webView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id _Nullable oldAgent, NSError * _Nullable error) {
            if (![oldAgent isKindOfClass:[NSString class]]) {
                // 为了避免没有获取到oldAgent，所以设置一个默认的userAgent
                // Mozilla/5.0 (iPhone; CPU iPhone OS 12_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148
                oldAgent = [NSString stringWithFormat:@"Mozilla/5.0 (%@; CPU iPhone OS %@ like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148", [[UIDevice currentDevice] model], [[[UIDevice currentDevice] systemVersion] stringByReplacingOccurrencesOfString:@"." withString:@"_"]];
            }
            
            //自定义user-agent
            if (![oldAgent hasSuffix:addAgent]) {
                NSString *newAgent = [oldAgent stringByAppendingFormat:@" DWD_HSQ/%@",addAgent];
                [[NSUserDefaults standardUserDefaults] registerDefaults:@{@"UserAgent":newAgent}];
                // 一定要设置customUserAgent，否则执行navigator.userAgent拿不到oldAgent
                webView.customUserAgent = newAgent;
            }
        }];
    });
}

    // 修改全局UserAgent值
    UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
    NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSString *newUserAgent = [userAgent stringByAppendingString:@" xxx"];//自定义需要拼接的字符串
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];