Add a Docker Compose setup with debugging and testing realm (#27)

Configure Keycloak to allow attaching a debugger (localhost:8081).

Add a testing realm with suitable example entries, and explain how to update and export the realm.

Reviewed-on: #27

testing/README.md

@@ -0,0 +1,56 @@
+# Creating a Testing Keycloak
+
+The Docker Compose setup in this directory sets up Keycloak and imports a realm `testing`.
+
+## Starting Keycloak
+
+Run `docker compose up -d` to start Keycloak. The admin console will be available at http://localhost:8080/.
+
+You can attach a Java debugger at `localhost:8081`.
+
+The realm export is in `import/testing.json`.
+It will be imported automatically when Keycloak starts.
+
+## Updating the Realm
+
+If you want to make changes to the testing realm and persist them, you need to export the realm.
+
+The following command runs the Keycloak export for the realm `testing` storing it in the mapped directory `import/testing.json`.
+The copying of the database is necessary to avoid locking errors.
+`env -i` makes sure the regular environment variables are not set to avoid port conflicts.
+
+```sh
+docker compose exec -it keycloak sh -c "cp -rp /opt/keycloak/data/h2 /tmp && env -i -- /opt/keycloak/bin/kc.sh export --db dev-file --db-url 'jdbc:h2:file:/tmp/h2/keycloakdb;NON_KEYWORDS=VALUE' --file /opt/keycloak/data/import/testing.json --realm testing"
+```
+
+## Testing Realm Configuration
+
+The realm contains these objects:
+
+* Clients:
+  * `export-dooris-ssh-keys` with secret `export-dooris-ssh-keys-secret` and role `export-dooris-ssh-keys`
+  * `export-mailing-list-addresses` with secret `export-mailing-list-addresses-secret` and role `export-mailing-list-addresses`
+* Realm Roles:
+  * `dooris-authorized`
+  * `mailing-list-chaos-member`
+  * `mailing-list-intern-member`
+  * `export-dooris-ssh-keys`
+  * `export-mailing-list-addresses`
+* Groups:
+  * `chaos` with role `mailing-list-chaos-member`
+  * `ìntern` with roles `dooris-authorized` and `mailing-list-intern-member`
+* Users:
+  * `tester` (Tony Tester), email `tester@example.com`, member of group `chaos`
+    * Mailing List Addresses:
+      * Chaos: `tester+chaos@example.com`
+      * Intern: `tester+intern@example.com`
+    * Dooris SSH Keys:
+      * SSH Key 1: `tester-ssh-key-1`
+      * SSH Key 2: `tester-ssh-key-2`
+  * `hacker` (Hans Acker), email `hacker@example.net`, member of groups `chaos`and `intern`
+      * Mailing List Addresses:
+          * Chaos: `hacker+chaos@example.net`
+          * Intern: `hacker+intern@example.net`
+      * Dooris SSH Keys:
+          * SSH Key 1: `hacker-ssh-key-1`
+          * SSH Key 2: `hacker-ssh-key-2`