feat(auth): add api key authentication

Implement API key authentication by introducing a new auth module.
Update configuration and .env.example to support API key setup, and add
authorization checks in the server endpoints.

.env.example

@@ -1,2 +1,3 @@
 PORT=11434
 VERBOSE=false
+API_KEY=MY0P3NA1K3Y

src/auth.ts

@@ -0,0 +1,38 @@
+/**
+ * @fileoverview This file contains the authentication logic for the server.
+ */
+import http from 'http';
+import { config } from './config';
+
+/**
+ * Checks for API key authentication.
+ * @param req - The HTTP incoming message object.
+ * @param res - The HTTP server response object.
+ * @returns True if the request is authorized, false otherwise.
+ */
+export function isAuthorized(
+  req: http.IncomingMessage,
+  res: http.ServerResponse,
+): boolean {
+  if (!config.API_KEY) {
+    return true; // No key configured, public access.
+  }
+
+  const authHeader = req.headers.authorization;
+  if (!authHeader) {
+    res.writeHead(401, { 'Content-Type': 'application/json' });
+    res.end(
+      JSON.stringify({ error: { message: 'Missing Authorization header' } }),
+    );
+    return false;
+  }
+
+  const token = authHeader.split(' ')[1];
+  if (token !== config.API_KEY) {
+    res.writeHead(401, { 'Content-Type': 'application/json' });
+    res.end(JSON.stringify({ error: { message: 'Invalid API key' } }));
+    return false;
+  }
+
+  return true;
+}

src/config.ts

@@ -23,4 +23,10 @@ export const config = {
    * @type {boolean}
    */
   VERBOSE: Boolean(process.env.VERBOSE ?? true),
+  /**
+   * The API key for securing the server.
+   * If not set, the server will be public.
+   * @type {string | undefined}
+   */
+  API_KEY: process.env.API_KEY,
 };

src/server.ts

@@ -8,6 +8,7 @@ import { listModels, sendChat, sendChatStream } from './chatwrapper';
 import { mapRequest, mapResponse, mapStreamChunk } from './mapper.js';
 import { RequestBody, GeminiResponse, GeminiStreamChunk, Part } from './types';
 import { config } from './config';
+import { isAuthorized } from './auth';
 
 // ==================================================================
 // Server Configuration
@@ -97,6 +98,10 @@ http
       return;
     }
 
+    if (!isAuthorized(req, res)) {
+      return;
+    }
+
     // Route for listing available models.
     if (pathname === '/v1/models' || pathname === '/models') {
       res.writeHead(200, { 'Content-Type': 'application/json' });