feat(proxy): add environment config and request handling

- Introduce environment-based configuration for proxy settings
- Add middleware for API key authentication
- Implement request forwarding to LanguageTool backend
- Set up server startup and routing logic

src/env.ts

@@ -0,0 +1,63 @@
+/**
+ * Environment configuration for lt-auth-proxy.
+ * All properties are lazily evaluated and cached on first access.
+ */
+
+export class Env {
+    private static _proxyHost?: string;
+    private static _proxyPort?: number;
+    private static _apiKeys?: string[];
+    private static _ltServerHost?: string;
+    private static _ltServerPort?: number;
+
+    private static getEnv(key: string, required = false): string | undefined {
+        const value = Deno.env.get(key);
+        if (required && (!value || value.trim() === '')) {
+            throw new Error(`Missing required environment variable: ${key}`);
+        }
+        return value;
+    }
+
+    /** Hostname for the proxy (default: 0.0.0.0) */
+    static get proxyHost(): string {
+        if (this._proxyHost === undefined) {
+            this._proxyHost = this.getEnv('PROXY_HOST') || '0.0.0.0';
+        }
+        return this._proxyHost;
+    }
+
+    /** Port for the proxy (default: 8011) */
+    static get proxyPort(): number {
+        if (this._proxyPort === undefined) {
+            this._proxyPort = Number(this.getEnv('PROXY_PORT') || 8011);
+        }
+        return this._proxyPort;
+    }
+
+    /** List of allowed API keys (required) */
+    static get apiKeys(): string[] {
+        if (this._apiKeys === undefined) {
+            const raw = this.getEnv('API_KEYS', true)!;
+            this._apiKeys = raw.split(',').map((k) => k.trim()).filter((k) =>
+                k.length > 0
+            );
+        }
+        return this._apiKeys;
+    }
+
+    /** Hostname of the LanguageTool backend (default: localhost) */
+    static get ltServerHost(): string {
+        if (this._ltServerHost === undefined) {
+            this._ltServerHost = this.getEnv('LT_SERVER_HOST') || 'localhost';
+        }
+        return this._ltServerHost;
+    }
+
+    /** Port of the LanguageTool backend (default: 8010) */
+    static get ltServerPort(): number {
+        if (this._ltServerPort === undefined) {
+            this._ltServerPort = Number(this.getEnv('LT_SERVER_PORT') || 8010);
+        }
+        return this._ltServerPort;
+    }
+}

src/ltProxyAuth.ts

@@ -0,0 +1,21 @@
+import { Middleware } from 'http-kernel/Types/mod.ts';
+import { Env } from './env.ts';
+
+/**
+ * Middleware that checks for a valid API key via ?apiKey=... query/form param.
+ * Rejects request with 403 if the key is missing or invalid.
+ */
+export const authMiddleware: Middleware = async (ctx, next) => {
+    const key = ctx.query.apiKey;
+
+    // Support both ?apiKey=... and form body with apiKey=...
+    const extractedKey = Array.isArray(key) ? key[0] : key;
+
+    if (!extractedKey || !Env.apiKeys.includes(extractedKey)) {
+        return new Response('Forbidden – Invalid API key', { status: 403 });
+    }
+
+    return await next();
+};
+
+export { authMiddleware as ltProxyAuth };

src/ltProxyHandler.ts

@@ -0,0 +1,28 @@
+import { Handler } from 'http-kernel/Types/mod.ts';
+import { Env } from './env.ts';
+
+/**
+ * Forwards the incoming request to the actual LanguageTool server.
+ * Dynamically passes through path and query string.
+ */
+export const handler: Handler = async (ctx) => {
+    const originalUrl = new URL(ctx.req.url);
+    const proxyUrl = new URL(
+        `${originalUrl.pathname}${originalUrl.search}`,
+        `http://${Env.ltServerHost}:${Env.ltServerPort}`,
+    );
+
+    const forwarded = await fetch(proxyUrl.toString(), {
+        method: ctx.req.method,
+        headers: ctx.req.headers,
+        body: ctx.req.body,
+    });
+
+    const headers = new Headers(forwarded.headers);
+    return new Response(forwarded.body, {
+        status: forwarded.status,
+        headers,
+    });
+};
+
+export { handler as ltProxyHandler };

src/main.ts

@@ -0,0 +1,19 @@
+import { HttpKernel } from 'http-kernel/mod.ts';
+import { Env } from './env.ts';
+import { ltProxyAuth } from './ltProxyAuth.ts';
+import { ltProxyHandler } from './ltProxyHandler.ts';
+
+const httpKernel = new HttpKernel();
+
+httpKernel.route({
+    method: 'POST',
+    path: '/*',
+}).middleware(ltProxyAuth).handle(ltProxyHandler);
+
+Deno.serve({
+    port: Env.proxyPort,
+    hostname: Env.proxyHost,
+    onListen: ({ hostname, port }) => {
+        console.info(`lt-auth-proxy listening on ${hostname}:${port}`);
+    },
+}, async (req) => await httpKernel.handle(req));