Enable passwordless sudo for the user

Currently admin user is part of the sudoers
group, adding the user for passwordless sudo
from this issue Azure#69

Signed-off-by: Bala Konda Reddy M <bala12352@gmail.com>

libazureinit/src/provision/user.rs

@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
-use std::process::Command;
+use std::{fs::Permissions, os::unix::fs::PermissionsExt, process::Command};
+
+use std::io::Write;
 
 use tracing::instrument;
 
@@ -88,11 +90,13 @@ pub enum Provisioner {
 
 impl Provisioner {
     pub(crate) fn create(&self, user: &User) -> Result<(), Error> {
-        match self {
+        let _ = match self {
             Self::Useradd => useradd(user),
             #[cfg(test)]
             Self::FakeUseradd => Ok(()),
-        }
+        };
+        let path = "/etc/sudoers.d/azure-init-user";
+        add_user_for_passwordless_sudo(user.name.clone(), path)
     }
 }
 
@@ -123,10 +127,39 @@ fn useradd(user: &User) -> Result<(), Error> {
     Ok(())
 }
 
+fn add_user_for_passwordless_sudo(
+    username: String,
+    path: &str,
+) -> Result<(), Error> {
+    // Create a file under /etc/sudoers.d with azure-init-user
+    let sudoers_path = path;
+    let mut sudoers_file = std::fs::OpenOptions::new()
+        .append(true)
+        .create(true)
+        .open(sudoers_path)?;
+    write!(
+        sudoers_file,
+        "{} ALL=(ALL) NOPASSWD: ALL \n",
+        username.to_string()
+    )?;
+    sudoers_file.flush()?;
+    // Set the permission
+    sudoers_file.set_permissions(Permissions::from_mode(0o600))?;
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
+    use std::{
+        fs::{self, Permissions},
+        os::unix::fs::PermissionsExt,
+    };
+
     use crate::User;
 
+    use super::add_user_for_passwordless_sudo;
+    const PATH: &str = "/tmp/test1";
+
     #[test]
     fn password_skipped_in_debug() {
         let user_with_password =
@@ -142,4 +175,17 @@ mod tests {
             format!("{:?}", user_without_password)
         );
     }
+
+    #[test]
+    fn test_user_insecure() {
+        let user_insecure = User::new("azureuser", []);
+        let a = add_user_for_passwordless_sudo(user_insecure.name, PATH);
+        assert!(a.is_ok());
+        assert!(fs::metadata(PATH).is_ok(), "Specified file not created");
+        assert_eq!(
+            fs::Permissions(PATH).mode(),
+            Permissions.mode(0o600),
+            "Permissions are not set properly"
+        );
+    }
 }