我正在Android Studio中使用following instructions生成多个APK：

android {
  ...
  splits {

    // Configures multiple APKs based on ABI.
    abi {

      // Enables building multiple APKs per ABI.
      enable true

      // By default all ABIs are included,so use reset() and include to specify that we only
      // want APKs for x86 and x86_64.

      // Resets the list of ABIs that Gradle should create APKs for to none.
      reset()

      // Specifies a list of ABIs that Gradle should create APKs for.
      include "x86","x86_64"

      // Specifies that we do not want to also generate a universal APK that includes all ABIs.
      universalApk false
    }
  }
}

问题是：如何为每个不同的APK分配不同的 keystore ？我在官方指南中找不到任何说明...