Add a separate client binary, with some common code to the server.

The cargo workspace thing was a PITA to figure out, but it seems to be working.  Could maybe be simplified?

client/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "client"
+version = "0.2.0"
+edition = "2021"
+
+[dependencies]
+clap = { version = "4.5.20", features = ["derive"] }
+common = { path = "../common" }

client/src/main.rs

@@ -0,0 +1,23 @@
+mod options;
+
+use crate::options::OPTIONS;
+use common::{read_string, Request};
+use std::os::unix::net::UnixStream;
+
+fn main() -> std::io::Result<()> {
+    let mut stream = UnixStream::connect(&OPTIONS.socket_name)?;
+    println!("Connected to server");
+
+    let request = Request {
+        userid: OPTIONS.username.clone(),
+        password: OPTIONS.password.clone(),
+        service: "ignore-this".to_string(),
+        realm: "also-ignore-this".to_string(),
+    };
+
+    request.write_to_stream(&mut stream)?;
+    let response = read_string(&mut stream)?;
+    println!("Response: {}", response);
+
+    Ok(())
+}

client/src/options.rs

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+use clap::Parser;
+use std::path::PathBuf;
+use std::sync::LazyLock;
+
+#[derive(Parser, Clone, Debug)]
+/// saslauthd test client
+pub struct Opt {
+    #[arg(
+        short = 'f',
+        long = "socket-name",
+        default_value = "/tmp/saslauthd.sock"
+    )]
+    pub socket_name: PathBuf,
+
+    #[arg(default_value = "bp")]
+    pub username: String,
+
+    #[arg(default_value = "some-rad-password")]
+    pub password: String,
+}
+
+pub static OPTIONS: LazyLock<Opt> = LazyLock::new(Opt::parse);