当请求HTTPS页面通过HTTP加载资源时，会出现混合内容"警告.

"Mixed Content" warnings occur when an HTTPS page is asked to load a resource over HTTP.

这很危险，因为不安全的资源容易受到主动攻击者的更改或被动攻击者的窃听，这违反了用户对HTTPS页面安全性的期望.

This is dangerous because the insecure resources are vulnerable to alteration by an active attacker or eavesdropping by a passive attacker, which violates the user's expectation of security for an HTTPS page.

https://developers.google.com/web/fundamentals/security/prevent-mixed-content/fixing-mixed-content?hl=zh-CN