因为我已经把所有的东西都转发到index.php了，所以我想我应该尝试用PHP而不是.htaccess文件来设置头文件，它成功了！耶！以下是我添加到index.php的内容，以供其他遇到此问题的人参考。

// Allow from any origin
if (isset($_SERVER['HTTP_ORIGIN'])) {
    // should do a check here to match $_SERVER['HTTP_ORIGIN'] to a
    // whitelist of safe domains
    header("Access-Control-Allow-Origin: {$_SERVER['HTTP_ORIGIN']}");
    header('Access-Control-Allow-Credentials: true');
    header('Access-Control-Max-Age: 86400');    // cache for 1 day
}
// Access-Control headers are received during OPTIONS requests
if ($_SERVER['REQUEST_METHOD'] == 'OPTIONS') {

    if (isset($_SERVER['HTTP_ACCESS_CONTROL_REQUEST_METHOD']))
        header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS");         

    if (isset($_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']))
        header("Access-Control-Allow-Headers: {$_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']}");

}

感谢slashingweapon在this question上给出的答案
因为我使用的是Slim，所以我添加了此路由，以便OPTIONS请求获得HTTP 200响应

// return HTTP 200 for HTTP OPTIONS requests
$app->map('/:x+', function($x) {
    http_response_code(200);
})->via('OPTIONS');

.htaccess不应该使用add而不是set吗？

Header add Access-Control-Allow-Origin "*"
Header add Access-Control-Allow-Methods: "GET,POST,OPTIONS,DELETE,PUT"

这就是我的工作：

Header add Access-Control-Allow-Origin "*"
Header add Access-Control-Allow-Headers "origin, x-requested-with, content-type"
Header add Access-Control-Allow-Methods "PUT, GET, POST, DELETE, OPTIONS"

在此答案Custom HTTP Header for a specific file中，您可以使用<File>为单个文件启用CORS，代码如下：

<Files "index.php">
  Header set Access-Control-Allow-Origin "*"
  Header set Access-Control-Allow-Methods: "GET,POST,OPTIONS,DELETE,PUT"
</Files>

您可以放置特定来源（协议+域+可选端口），而不是"*"。

将工作100%，应用于.htaccess：

# Enable cross domain access control
SetEnvIf Origin "^http(s)?://(.+\.)?(1xyz\.com|2xyz\.com)$" REQUEST_ORIGIN=$0
Header always set Access-Control-Allow-Origin %{REQUEST_ORIGIN}e env=REQUEST_ORIGIN
Header always set Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS"
Header always set Access-Control-Allow-Headers "x-test-header, Origin, X-Requested-With, Content-Type, Accept"

# Force to request 200 for options
RewriteEngine On
RewriteCond %{REQUEST_METHOD} OPTIONS
RewriteRule .* / [R=200,L]

看起来你使用的是slim（2.x）的旧版本。你可以只在.htaccess中添加以下行，而不需要在PHP脚本中做任何事情。

# Enable cross domain access control
SetEnvIf Origin "^http(s)?://(.+\.)?(domain_one\.com|domain_two\.net)$" REQUEST_ORIGIN=$0
Header always set Access-Control-Allow-Origin %{REQUEST_ORIGIN}e env=REQUEST_ORIGIN
Header always set Access-Control-Allow-Methods "GET, POST, PUT, DELETE"
Header always set Access-Control-Allow-Headers: Authorization

# Force to request 200 for options
RewriteEngine On
RewriteCond %{REQUEST_METHOD} OPTIONS
RewriteRule .* / [R=200,L]

多亏了迪文，我为我的SLIM应用程序找到了多域访问的解决方案。
在htaccess中：

SetEnvIf Origin "http(s)?://(www\.)?(allowed.domain.one|allowed.domain.two)$" AccessControlAllowOrigin=$0$1
Header set Access-Control-Allow-Origin %{AccessControlAllowOrigin}e env=AccessControlAllowOrigin
Header set Access-Control-Allow-Credentials true

在index.php中

// Access-Control headers are received during OPTIONS requests
if ($_SERVER['REQUEST_METHOD'] == 'OPTIONS') {

    if (isset($_SERVER['HTTP_ACCESS_CONTROL_REQUEST_METHOD']))
        header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS");         

    if (isset($_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']))
        header("Access-Control-Allow-Headers: {$_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']}");
}
// instead of mapping:
$app->options('/(:x+)', function() use ($app) {
    //...return correct headers...
    $app->response->setStatus(200);
});

我尝试了@abimelex解决方案，但在Slim 3.0中，MapOPTIONS请求如下所示：

$app = new \Slim\App();
$app->options('/books/{id}', function ($request, $response, $args) {
    // Return response headers
});

https://www.slimframework.com/docs/objects/router.html#options-route

对于ubuntu用户：
您必须使用以下命令首先激活标头模块：

sudo a2enmod headers

然后通过以下方式重新启动Apache：

sudo service apache2 restart

然后将以下头文件添加到htaccess中：

Header set Access-Control-Allow-Origin "*"
Header set Access-Control-Allow-Headers "origin, x-requested-with, content-type"
Header set Access-Control-Allow-Methods "PUT, GET, POST, DELETE, OPTIONS"