Set hadoop system user for client embedded in Java webapp

Finally I stumbled on the constant

static final String HADOOP_USER_NAME = "HADOOP_USER_NAME";`

in the UserGroupInformation class.

Setting this either as an environment variable, as a Java system property on startup (using -D) or programmatically with System.setProperty("HADOOP_USER_NAME", "hduser"); makes Hadoop use whatever username you want for connecting to the remote Hadoop cluster.

The code below works for me the same as

System.setProperty("HADOOP_USER_NAME", "hduser")

UserGroupInformation ugi = UserGroupInformation.createRemoteUser("hduser"); 
ugi.doAs(new PrivilegedExceptionAction<Void>() {
    public Void run() throws Exception {
        Configuration configuration = new Configuration(); 
        configuration.set("hadoop.job.ugi", "hduser");
        int res = ToolRunner.run(configuration, new YourTool(), args);
        return null; 
    }
});