Establish project foundation and shared utilities

src/errors/unauthorized-error.ts

@@ -0,0 +1,10 @@
+/** Authentication failure whose message is safe to return to clients. */
+export class UnauthorizedError extends Error {
+    /**
+     * @param message - Client-safe unauthorized summary.
+     */
+    constructor(message = 'Unauthorized') {
+        super(message);
+        this.name = 'UnauthorizedError';
+    }
+}