Runas python subprocess

Question

I use the code I find all over stackoverflow to run a runas program in Python:

import subprocess as sp

prog = sp.Popen(
    ['runas', '/user:"[email protected]"', '/netonly', '"C:\foo\bar.bat"'], stdin=sp.PIPE
)
ww = "p@ssw0rd".encode("utf-8")
prog.stdin.write(ww)
prog.communicate()

Some remarks before the problem:

• it is not unsafe, in production I can safe the password in a Key Vault and retrieve it when used
• we cannot change the authorization method, we have to connect with some external AD for... reasons

In cmd, the C:\foo\bar.bat asks for password and then works fine:

However, with subprocess I keep getting:

Enter the password for "[email protected]":
RUNAS ERROR: Unable to acquire user password

What am I doing wrong? I reckon it's a newline / return error or something?