跨域访问设置方式

header('Access-Control-Allow-Origin: *');//允许跨域域名
header('Access-Control-Allow-Methods: GET, POST, PATCH, PUT, OPTIONS, DELETE');//允许跨域方式
header('Access-Control-Allow-Headers: *');//允许header
header('Access-Control-Expose-Headers: *');//某些header无法传递，须要指明header白名单（content-type 就在此列）