do some major refactoring and add a lot more features

Dockerfile

@@ -1,19 +1,32 @@
-ARG         ALPINE_VERSION=${ALPINE_VERSION:-3.9}
-FROM        alpine:${ALPINE_VERSION}
+ARG         ALPINE_VERSION="${ALPINE_VERSION:-3.9}"
+FROM        alpine:"${ALPINE_VERSION}"
 
 LABEL       maintainer="https://github.com/hermsi1337"
 
-ARG         OPENSSH_VERSION=${OPENSSH_VERSION:-7.9_p1-r5}
-ENV         OPENSSH_VERSION=${OPENSSH_VERSION} \
-            ROOT_PASSWORD=root \
-            KEYPAIR_LOGIN=false
+ARG         OPENSSH_VERSION="${OPENSSH_VERSION:-7.9_p1-r5}"
+ENV         CONF_VOLUME="/conf.d"
+ENV         OPENSSH_VERSION="${OPENSSH_VERSION}" \
+            CACHED_SSH_DIRECTORY="${CONF_VOLUME}/ssh" \
+            AUTHORIZED_KEYS_VOLUME="${CONF_VOLUME}/authorized_keys" \
+            ROOT_KEYPAIR_LOGIN_ENABLED="false" \
+            ROOT_LOGIN_UNLOCKED="false" \
+            USER_LOGIN_SHELL="/bin/bash" \
+            USER_LOGIN_SHELL_FALLBACK="/bin/ash"
+
+RUN         apk add --upgrade --no-cache \
+                    bash \
+                    bash-completion \
+                    rsync \
+                    openssh=${OPENSSH_VERSION} \
+            && \
+            mkdir -p /root/.ssh "${CONF_VOLUME}" "${AUTHORIZED_KEYS_VOLUME}" \
+            && \
+            cp -a /etc/ssh "${CACHED_SSH_DIRECTORY}" \
+            && \
+	        rm -rf /var/cache/apk/*
 
 COPY        entrypoint.sh /
-RUN         apk add --upgrade --no-cache openssh=${OPENSSH_VERSION} \
-            && chmod +x /entrypoint.sh \
-	    && mkdir -p /root/.ssh \
-	    && rm -rf /var/cache/apk/* /tmp/*
-
+COPY        conf.d/etc/ /etc/
 EXPOSE      22
 VOLUME      ["/etc/ssh"]
 ENTRYPOINT  ["/entrypoint.sh"]