Specifies whether it is acceptable to communicate with a repository over an insecure HTTP connection.
For security purposes this intentionally requires a user to opt-in to using insecure protocols on case by case basis.
Gradle intentionally does not offer a global system/gradle property that allows a universal disable of this check.

配置Android Gradle时如果有http的仓库地址会出现这个错误，升级gradle7.0后提示的，解决办法：

maven {
    allowInsecureProtocol = true
    // libflutter.so 和 libflutter.jar 仓库地址
    url 'http://download.flutter.io'
}

以上。