[Yarn] How to set user in ContainerLaunchContext?

[Peter Rudenko]

Hi, i have an ApplicationMaster which accepts requests and launches 
container on which it launches spark-submit --master yarn. In request i 
have a field "username" - the user i want to laucnh a job from. How can 
i set a user which will be run conmmand on a container? Currently they 
all running as yarn user even though AM is running as a root user.

Here's my code:

private def setupTokens(username:String): ByteBuffer = {
  val credentials = UserGroupInformation.createProxyUser(username, 
UserGroupInformation.getCurrentUser).getCredentials
  val dob =new DataOutputBuffer();
  credentials.writeTokenStorageToStream(dob);
  ByteBuffer.wrap(dob.getData(),0, dob.getLength()).duplicate();
}

val cCLC = Records.newRecord(classOf[ContainerLaunchContext])

cCLC.setCommands(List("spark-submit --master yarn ..."))

cCLC.setTokens(setupTokens(user))

Thanks, Peter Rudenko