Build fail maybe because of firewall (add-apt-repository)

[KyleJeong]

In my company environment, we have to use proxy.

So I had to modify the ubuntu_circuit_training file like this.

APT_COMMAND="apt-get -o Acquire::Retries=10 -o Acquire::http::Proxy="http://companyproxyip:8080" -o Acquire::https::Pr
    oxy="http://companyproxyip:8080" -y"

It made me to run this line successfully.

# Installs basics including add-apt.
RUN ${APT_COMMAND} update && ${APT_COMMAND} install -y --no-install-recommends \
        software-properties-common \
        curl \
        tmux \
        vim \
        less

But I can't run this repository stuff.

# Adds repository to pull versions of python from.
RUN add-apt-repository ppa:deadsnakes/ppa

I met this error message

 > [ 4/17] RUN add-apt-repository ppa:deadsnakes/ppa:
2.855 Cannot add PPA: 'ppa:~deadsnakes/ubuntu/ppa'.
2.855 ERROR: '~deadsnakes' user or team does not exist.

I figured out that was related with proxy. I tried several way like as ENV command(http_proxy variable) or COPY command(/etc/apt copy), but not successful till now.
Is there anyone who solved this issue?

I'm running on Ubuntu 20.04 env.

Thank you in advance.