什么是ATS功能?
ATS是iOS9和OS X El Capitan的一个新特性。开启该功能后，ATS对使用NSURLConnection, CFURL或NSURLSession 等APIs 进行的网络请求默认强制使用HTTPS加密传输，目标是提高Apple 操作系统以及应用程序的安全性。
WWDC 16 中，Apple 表示将继续在 iOS 10 和OS X 10.12 中持续收紧对普通 HTTP站点的访问限制。从 2017 年 1 月 1 日起，所有新提交到appstore中的 app 默认都将不再允许使用 NSAllowsArbitraryLoads 来绕过 ATS 限制的。也就是说，我们最好保证 与app 通讯的所有网络服务器都部署了 HTTPS 加密的，否则可能会在应用审核时遇到大麻烦。
苹果公司官方文章指出，https必须符合ATS要求，服务器必须支持传输层安全(TLS)协议1.2以上版本;证书必须使用SHA256或更高的 哈希算法签名，并使用2048位以上RSA密钥或256位以上ECC算法;使用安全度更高的ECDHE加密套件。下面是苹果官方要求的3点关于SSL的技 术要点：
Requirements for Connecting Using ATS
With ATS fully enabled, your app’s HTTP connections must use HTTPS and must satisfy the following security requirements:
The server certificate must meet at least one of the following trust requirements:
Issued by a certificate authority (CA) whose root certificate is incorporated into the operating system
Issued by a trusted root CA and installed by the user or a system administrator
The negotiated Transport Layer Security version must be TLS 1.2
The negotiated TLS connection cipher suite must support forward secrecy (FS) and be one of the following:
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
The leaf server certificate must be signed with one of the following types of keys:
Rivest-Shamir-Adleman (RSA) key with a length of at least 2048 bits
Elliptic-Curve Cryptography (ECC) key with a size of at least 256 bits
In addition, the leaf server certificate hashing algorithm must be Secure Hash Algorithm 2 (SHA-2) with a digest length of at least 256 (that is, SHA-256 or greater).
If ATS is not enabled, the system still performs HTTPS server trust evaluation but you can override it on a case-by-case basis, as described in HTTPS Server Trust Evaluation. With ATS fully enabled, you cannot override the default HTTPS server trust evaluation.
其中需要证书必须使用SHA256或更高的哈希算法签名，并使用2048位以上RSA密钥或256位以上ECC算法证书。支持TLS1.2协议和ECDHE算法需要在 Services端做相应的调整。
Nginx中，需要修改nginx.conf，在其中SSL部分修改配置：
server {
listen 443;
server_name localhost;
ssl on;
ssl_certificate yourdomain_bundle.crt;
ssl_certificate_key yourdomain.key;
ssl_session_timeout 5m;
ssl_session_cache shared:SSL:1m;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers ECDH:AESGCM:HIGH:!RC4:!DH:!MD5:!aNULL:!eNULL;
location / {
root html;
index index.html index.htm;
}
}
由于容器的一些限制，在解决IOS ATS适配SSL的问题上面推荐使用apache和nginx来安装证书，同时openssl的版本建议使用 1.0.1+,因为openssl在1.0.1以后才开始支持TLSv1.2协议，介于一些其他漏洞的因素，openssl版本 官方推荐使用1.0.1g+版本.