build: set up workflow to get my Apple Music user token

frontend/esbuild.js

···
       };
       const url = new URL(`http://localhost${req.url}`);
       const route =
-        url.pathname === "/" || url.pathname === "/scrobbles"
+        url.pathname === "/" || url.pathname === "/dev/am-auth-flow"
           ? { hostname: "127.0.0.1", port: 8080 }
           : { hostname: hosts[0], port };
       const routedOptions = { ...options, ...route };

justfile

···
 
 [working-directory: 'frontend']
 serve-js:
-	npm start
+	watchexec --restart --watch esbuild.js npm start
 
 [working-directory: 'server']
 serve-rs $RUST_LOG=env('RUST_LOG', 'debug,selectors=warn,html5ever=warn'):

server/src/am_auth_flow.rs

···
+use askama::Template;
+
+use crate::scrapers::apple_music;
+
+#[derive(Template, Debug, Clone)]
+#[template(path = "am-auth-flow.html")]
+pub struct AuthFlowTemplate {
+    token: String,
+}
+
+impl AuthFlowTemplate {
+    pub fn new() -> anyhow::Result<Self> {
+        let token = apple_music::build_developer_token()?;
+        Ok(Self { token })
+    }
+}

server/src/main.rs

···
+#[cfg(debug_assertions)]
+mod am_auth_flow;
 mod index;
 mod scrapers;
 
 use std::net::SocketAddr;
 
+#[cfg(debug_assertions)]
+use crate::am_auth_flow::AuthFlowTemplate;
 use crate::index::RootTemplate;
 
 use askama::Template;
···
 
     let app = Router::new()
         .route("/", get(render_index_handler))
+        .route("/dev/am-auth-flow", get(render_apple_music_auth_flow))
         .fallback(get_service(ServeDir::new(".")))
         .layer(
             ServiceBuilder::new()
···
         StatusCode::INTERNAL_SERVER_ERROR
     })
 }
+
+async fn render_apple_music_auth_flow() -> impl IntoResponse {
+    #[cfg(not(debug_assertions))]
+    return StatusCode::NOT_FOUND;
+
+    #[cfg(debug_assertions)]
+    {
+        let template = AuthFlowTemplate::new();
+        template
+            .and_then(|template| Ok(template.render()?))
+            .map(Html)
+            .map_err(|err| {
+                tracing::error!("failed to render Apple Music auth flow: {err:?}");
+                StatusCode::INTERNAL_SERVER_ERROR
+            })
+    }
+}

server/src/scrapers/apple_music.rs

···
 
 impl AppleMusic {
     pub async fn fetch() -> anyhow::Result<Self> {
-        let mut header = Header::new(Algorithm::ES256);
-        header.kid = Some(
-            env::var("APPLE_DEVELOPER_TOKEN_KEY_ID").context("missing apple developer key ID")?,
-        );
-        let team_id =
-            env::var("APPLE_DEVELOPER_TOKEN_TEAM_ID").context("missing apple developer team ID")?;
-        let claims = Claims::new(team_id);
-        let auth_key = env::var("APPLE_DEVELOPER_TOKEN_AUTH_KEY")
-            .context("missing apple developer auth key")?;
-        let key = EncodingKey::from_ec_pem(auth_key.as_bytes())
-            .context("failed to parse appple developer auth key")?;
-        let jwt = jsonwebtoken::encode(&header, &claims, &key)
-            .context("failed to encode apple developer JWT")?;
+        let jwt = build_developer_token()?;
         let user_token = env::var("APPLE_USER_TOKEN").context("missing apple user token")?;
 
         let client = Client::new();
···
         .map_err(|error| tracing::warn!(?error, "failed to call Apple Music"))
         .ok()
 }
+
+pub fn build_developer_token() -> anyhow::Result<String> {
+    let mut header = Header::new(Algorithm::ES256);
+    header.kid =
+        Some(env::var("APPLE_DEVELOPER_TOKEN_KEY_ID").context("missing apple developer key ID")?);
+    let team_id =
+        env::var("APPLE_DEVELOPER_TOKEN_TEAM_ID").context("missing apple developer team ID")?;
+    let claims = Claims::new(team_id);
+    let auth_key =
+        env::var("APPLE_DEVELOPER_TOKEN_AUTH_KEY").context("missing apple developer auth key")?;
+    let key = EncodingKey::from_ec_pem(auth_key.as_bytes())
+        .context("failed to parse appple developer auth key")?;
+
+    jsonwebtoken::encode(&header, &claims, &key).context("failed to encode apple developer JWT")
+}

server/templates/am-auth-flow.html

···
+<!doctype html>
+<html>
+  <head>
+    <title>cherry.computer's Apple Music Sign-In</title>
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="apple-music-developer-token" content={{ token }} />
+    <meta name="apple-music-app-name" content="cherry.computer sign-in" />
+    <meta name="apple-music-app-build" content="1.0" />
+    <script src="https://js-cdn.music.apple.com/musickit/v3/musickit.js" async></script>
+    <script>
+      document.addEventListener('musickitloaded', async function () {
+        const music = MusicKit.getInstance();
+        const userToken = await music.authorize();
+
+        const codeEl = document.createElement("code");
+        codeEl.textContent = userToken;
+        document.body.appendChild(codeEl);
+      });
+    </script>
+  </head>
+  <body>
+  </body>
+</html>