Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password)
fatal: Could not read from remote repository.

docker build . --build-arg priv_key="$(cat ~/.ssh/id_rsa)" --build-arg pub_key="$(cat ~/.ssh/id_rsa.pub)"

FROM centos/python-35-centos7:latest
USER root
ARG pub_key
ARG priv_key
RUN mkdir -p /root/.ssh/
RUN chmod 0700 /root/.ssh/
RUN echo ${pub_key} >> /root/.ssh/id_rsa.pub
RUN chmod 600 /root/.ssh/id_rsa.pub
RUN echo ${priv_key} >> /root/.ssh/id_rsa
RUN chmod 600 /root/.ssh/id_rsa
RUN git config --global user.name "A name"
RUN git config --global user.email "email@address.com"
RUN echo "Host 192.168.1.28ntPasswordAuthentication non" >> /root/.ssh/config
RUN chmod 600 /root/.ssh/config
RUN ssh-keyscan -t rsa 192.168.1.28 >> /root/.ssh/known_hosts
RUN ssh -Tv git@192.168.1.28

debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: read_passphrase: can't open /dev/tty: No such device or address
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Trying private key: /root/.ssh/id_ed25519

debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: Authentication succeeded (publickey).
Authenticated to 192.168.1.28 ([192.168.1.28]:22).

FROM ubuntu as intermediate > FROM centos:7
apt-get update > yum update
apt-get install -y git > yum install -y git

FROM centos/python-35-centos7:latest
#FROM centos:7
USER root
RUN yum update -y
RUN yum install -y git
ARG SSH_PRIVATE_KEY
RUN mkdir /root/.ssh/
RUN echo "${SSH_PRIVATE_KEY}" > /root/.ssh/id_rsa
RUN chmod 600 /root/.ssh/id_rsa
RUN touch /root/.ssh/known_hosts
RUN ssh-keyscan 192.168.1.28 >> /root/.ssh/known_hosts
RUN ssh -Tv git@192.168.1.28