[android] How to sign an application with a system certificate?

Question

Android

Hello. The task is this - you need to connect to the company's server using the L2TP + PSK protocol. For this, an android application was created. As it turned out from the search on the Internet, for the normal operation of the connections created in the application, the presence of the line android: sharedUserId="android.uid.system" in the manifest is necessary. However, in order for an application with this mode to be installed, it is necessary that the apk be signed with a system certificate, and each manufacturer has its own. The question is, who knows the links or at least an e-mail where you can find out the procedure for obtaining a certificate with which android.uid.system will work, and at least the approximate time frame for obtaining such a certificate.
PS For those who suggest using PPtP, I will explain - pptp in android versions less than 2.3.6 only works with encryption disabled, which is unacceptable in our case.

Answer 1

Firstly, this is called a "system signature", there was already a discussion here.
Second, use the key from /build/target/product/security/ and add android:sharedUserId="android.uid.system" to the AndroidManifest.xml file.
If that doesn't work, then you need to dig deeper...