Add a playbook to deploy an authenticating Pulp proxy

There is currently no practical, secure way to provide credentials for
accessing Ark's authenticated package repositories from within a Kolla
build.  Docker provides build secrets, but these must be explicitly
requested for each RUN statement, making them challenging to use in
Kolla.

This change adds a playbook that deploys an Nginx container that runs as
a reverse proxy, injecting an HTTP basic authentication header into
requests.

Because this proxy bypasses Pulp's authentication, it must not be
exposed to any untrusted environment.

[1] https://docs.docker.com/build/building/secrets/

Author: markgoddard

etc/kayobe/ansible/pulp-auth-proxy.yml

@@ -0,0 +1,14 @@
+---
+# See roles/pulp_auth_proxy/README.md for details.
+
+- name: Deploy Pulp auth proxy
+  hosts: container-image-builders
+  gather_facts: false
+  tasks:
+    - import_role:
+        name: pulp_auth_proxy
+      vars:
+        pulp_auth_proxy_url: "{{ stackhpc_repo_mirror_url }}"
+        pulp_auth_proxy_username: "{{ stackhpc_repo_mirror_username }}"
+        pulp_auth_proxy_password: "{{ stackhpc_repo_mirror_password }}"
+        pulp_auth_proxy_conf_path: "{{ base_path }}/containers/pulp_proxy"

etc/kayobe/ansible/roles/pulp_auth_proxy/README.md

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+# Pulp Auth Proxy
+
+There is currently no practical, secure way to provide credentials for
+accessing Ark's authenticated package repositories from within a Kolla build.
+Docker provides [build
+secrets](https://docs.docker.com/build/building/secrets/), but these must be
+explicitly requested for each RUN statement, making them challenging to use in
+Kolla.
+
+This role deploys an Nginx container that runs as a reverse proxy, injecting an
+HTTP basic authentication header into requests.
+
+Because this proxy bypasses Pulp's authentication, it must not be exposed to
+any untrusted environment.
+
+## Role variables
+
+* `pulp_auth_proxy_pulp_url`: URL of the Pulp server to proxy requests to.
+* `pulp_auth_proxy_username`: Username of the Pulp server to proxy requests to.
+* `pulp_auth_proxy_password`: Password of the Pulp server to proxy requests to.
+* `pulp_auth_proxy_conf_path`: Path to a directory in which to write Nginx
+  configuration.
+* `pulp_auth_proxy_listen_ip`: IP address on the Docker host on which to
+  listen. Default is `127.0.0.1`.
+* `pulp_auth_proxy_listen_port`: Port on the Docker host on which to listen.
+  Default is 80.

etc/kayobe/ansible/roles/pulp_auth_proxy/defaults/main.yml

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+---
+pulp_auth_proxy_url:
+pulp_auth_proxy_username:
+pulp_auth_proxy_password:
+pulp_auth_proxy_conf_path:
+pulp_auth_proxy_listen_ip: 127.0.0.1
+pulp_auth_proxy_listen_port: 80

etc/kayobe/ansible/roles/pulp_auth_proxy/tasks/main.yml

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+---
+- name: "Ensure {{ pulp_auth_proxy_conf_path }} exists"
+  ansible.builtin.file:
+    path: "{{ pulp_auth_proxy_conf_path }}"
+    state: directory
+    mode: 0700
+  become: true
+
+- name: Ensure pulp_proxy.conf is templated
+  ansible.builtin.template:
+    src: pulp_proxy.conf.j2
+    dest: "{{ pulp_auth_proxy_conf_path }}/pulp_proxy.conf"
+    mode: 0600
+  become: true
+  register: pulp_proxy_conf
+
+- name: Ensure pulp_proxy container is running
+  community.docker.docker_container:
+    name: pulp_proxy
+    image: nginx:stable-alpine
+    ports:
+      - "{{ pulp_auth_proxy_listen_ip }}:{{ pulp_auth_proxy_listen_port }}:80"
+    restart_policy: "no"
+    restart: "{{ pulp_proxy_conf is changed }}"
+    volumes:
+      - "{{ pulp_auth_proxy_conf_path }}/pulp_proxy.conf:/etc/nginx/conf.d/default.conf:ro"

etc/kayobe/ansible/roles/pulp_auth_proxy/templates/pulp_proxy.conf.j2

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+server {
+    listen {{ pulp_auth_proxy_listen_port }};
+    server_name pulp_proxy;
+    location / {
+        proxy_pass {{ pulp_auth_proxy_url }};
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header Host {{ pulp_auth_proxy_url | urlsplit('hostname') }};
+        # The important part: add basic auth header
+        proxy_set_header Authorization "Basic {{ (pulp_auth_proxy_username ~ ':' ~ pulp_auth_proxy_password) | b64encode }}";
+        proxy_pass_header Authorization;
+        # See https://stackoverflow.com/questions/25329941/nginx-caching-proxy-fails-with-ssl23-get-server-hellosslv3-alert-handshake-fail/25330027#25330027
+        proxy_ssl_server_name on;
+        proxy_ssl_protocols TLSv1.2;
+    }
+}