Run the tests with an Ubuntu image

The system is more complete, though much heavier. This lets us use PAM, which
is required for testing keyboard-interactive authentication.

spec/Dockerfile

@@ -1,8 +1,8 @@
-FROM alpine:3.7
+FROM ubuntu:latest
 
-RUN apk add openssh --no-cache
+RUN apt-get update && apt-get install -y openssh-server
 
-RUN adduser -D alice && (echo alice:alice | chpasswd)
+RUN useradd -m alice && (echo alice:alice | chpasswd)
 COPY id_ecdsa id_ecdsa.pub id_ed25519 id_ed25519.pub /home/alice/.ssh/
 RUN cat /home/alice/.ssh/id_ecdsa.pub /home/alice/.ssh/id_ed25519.pub > /home/alice/.ssh/authorized_keys
 COPY ssh_host_ecdsa_key ssh_host_ecdsa_key.pub ssh_host_ed25519_key ssh_host_ed25519_key.pub /etc/ssh/
@@ -14,4 +14,4 @@ RUN chmod 600 /home/alice/.ssh/* \
 COPY sshd_config /etc/ssh/sshd_config
 
 EXPOSE 22
-CMD ["/usr/sbin/sshd", "-D", "-e"]
+CMD ["service", "ssh", "start", "-D", "-e"]

spec/sshd_config

@@ -1,5 +1,6 @@
 AuthorizedKeysFile .ssh/authorized_keys
 
+UsePAM yes
 ChallengeResponseAuthentication no
 PasswordAuthentication yes
 PermitEmptyPasswords no