Add default config for debian, use systemd-creds by default

.gitignore

@@ -1,6 +1,7 @@
 # Rust
 /target
 config.toml
+!assets/debian/config.toml
 
 # Nix
 /.direnv/

Cargo.toml

@@ -85,9 +85,9 @@ assets = [
         "755",
     ],
     [
-        "example-config.toml",
+        "assets/debian/config.toml",
         "etc/muscl/config.toml",
-        "600",
+        "644",
     ],
     [
         "assets/completions/_*",

README.md

@@ -45,6 +45,28 @@ FLUSH PRIVILEGES;
 
 Now you should add the login credentials to the muscl configuration file, typically located at `/etc/muscl/config.toml`.
 
+### Setting the myscl password with `systemd-creds`
+
+The debian package assumes that you will provide the password for `muscl`'s database user with `systemd-creds`.
+
+You can add the password like this (run as root):
+
+```bash
+# Unless you already have a working credential store, you need to set it up first
+mkdir -p /etc/credstore.encrypted
+systemd-creds setup
+
+# Now set the muscl mysql password
+# Be careful not to leave the password in your shell history!
+systemd-creds encrypt --name=muscl_mysql_password <(echo "<strong_password_here>") /etc/credstore.encrypted/muscl_mysql_password
+```
+
+If you are running systemd older than version 254 (see `systemctl --version`), you might have to override the service to point to the path of the credential manually, because `ImportCredential=` is not supported. Run `systemctl edit muscl.service` and add the following line:
+
+```ini
+LoadEncyptedCredential=muscl_mysql_password:/etc/credstore.encrypted/muscl_mysql_password
+```
+
 ### NixOS
 
 For NixOS, there is a module available via the nix flake. You can include it in your configuration like this:

assets/debian/config.toml

@@ -0,0 +1,23 @@
+[mysql]
+# Hostname and port of the database.
+host = "localhost"
+port = 3306
+
+# The path to the unix socket of the database.
+# If you uncomment this line, the host and port will be ignored
+
+# socket_path = "/run/mysql/mysql.sock"
+
+# The username and password for the database connection.
+# The username and password can be omitted if you are connecting
+# to the database using socket based authentication.
+# However, the vendored systemd service is running as DynamicUser,
+# so these need to be specified by default unless you override the
+# systemd unit.
+username = "muscl"
+# This file gets created by systemd automatically, given you have set
+# the password with `systemd-creds`.
+password_file = "/run/credentials/muscl.service/muscl_mysql_password"
+
+# Database connection timeout in seconds
+timeout = 2

assets/systemd/muscl.service

@@ -17,6 +17,8 @@ DynamicUser=yes
 
 ConfigurationDirectory=muscl
 
+ImportCredential=muscl_mysql_password
+
 # This is required to read unix user/group details.
 PrivateUsers=false
 

nix/module.nix

@@ -135,6 +135,7 @@ in
           cfg.settings.mysql.socket_path
         ];
 
+        ImportCredential = "";
         LoadCredential = lib.mkIf (cfg.settings.mysql.passwordFile != null) [
           "mysql-password:${cfg.settings.mysql.passwordFile}"
         ];