feat(backend): initial setup for cms backend service

backend/src/services/gitea.service.ts

@@ -0,0 +1,112 @@
+import crypto from 'crypto';
+import { env } from '../config/env.js';
+
+interface GiteaUser {
+  id: number;
+  login: string;
+  email: string;
+  full_name: string;
+  avatar_url: string;
+}
+
+interface OAuthTokenResponse {
+  access_token: string;
+  token_type: string;
+  expires_in: number;
+  refresh_token?: string;
+}
+
+export class GiteaService {
+  private giteaUrl: string;
+  private clientId: string;
+  private clientSecret: string;
+  private redirectUri: string;
+  private allowedUsers: Set<string>;
+
+  constructor() {
+    this.giteaUrl = env.GITEA_URL;
+    this.clientId = env.GITEA_CLIENT_ID;
+    this.clientSecret = env.GITEA_CLIENT_SECRET;
+    this.redirectUri = env.GITEA_REDIRECT_URI;
+
+    const allowed = env.GITEA_ALLOWED_USERS;
+    this.allowedUsers = new Set(allowed.split(',').map(u => u.trim()).filter(Boolean));
+  }
+
+  /**
+   * Generate OAuth authorization URL
+   */
+  getAuthorizationUrl(state: string): string {
+    const params = new URLSearchParams({
+      client_id: this.clientId,
+      redirect_uri: this.redirectUri,
+      response_type: 'code',
+      state,
+      scope: 'read:user',
+    });
+
+    return `${this.giteaUrl}/login/oauth/authorize?${params.toString()}`;
+  }
+
+  /**
+   * Exchange authorization code for access token
+   */
+  async exchangeCodeForToken(code: string): Promise<OAuthTokenResponse> {
+    const response = await fetch(`${this.giteaUrl}/login/oauth/access_token`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Accept': 'application/json',
+      },
+      body: JSON.stringify({
+        client_id: this.clientId,
+        client_secret: this.clientSecret,
+        code,
+        redirect_uri: this.redirectUri,
+        grant_type: 'authorization_code',
+      }),
+    });
+
+    if (!response.ok) {
+      throw new Error(`Failed to exchange code: ${response.statusText}`);
+    }
+
+    return await response.json();
+  }
+
+  /**
+   * Fetch user info from Gitea using access token
+   */
+  async getUserInfo(accessToken: string): Promise<GiteaUser> {
+    const response = await fetch(`${this.giteaUrl}/api/v1/user`, {
+      headers: {
+        'Authorization': `Bearer ${accessToken}`,
+        'Accept': 'application/json',
+      },
+    });
+
+    if (!response.ok) {
+      throw new Error(`Failed to fetch user info: ${response.statusText}`);
+    }
+
+    return await response.json();
+  }
+
+  /**
+   * Check if user is allowed to access the CMS
+   */
+  isUserAllowed(username: string): boolean {
+    // If no allowed users specified, allow all
+    if (this.allowedUsers.size === 0) {
+      return true;
+    }
+    return this.allowedUsers.has(username);
+  }
+
+  /**
+   * Generate random state for CSRF protection
+   */
+  generateState(): string {
+    return crypto.randomBytes(32).toString('hex');
+  }
+}