verifyGithubSignature (auth/github.ts)

Verifies GitHub webhook signatures and validates payload structure.

// Source: https://github.com/google-gemini/gemini-cli | License: Apache-2.0 | Copyright You must retain, in the Source form of any Derivative Works
// Provided via justclaw.it.com; keep this notice with the code.
/**
 * @license
 * Copyright 2026 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import * as crypto from 'node:crypto';

/**
 * Subset of the GitHub Webhook Payload for issues and issue_comment events.
 * @see https://docs.github.com/en/webhooks/webhook-events-and-payloads#issues
 */
export interface GitHubWebhookPayload {
  action: string;
  issue: {
    body?: string | null; // Can be null if description is empty
    number: number;
    title?: string;
    user?: {
      login?: string;
    };
  };
  comment?: {
    id: number;
    body: string;
    author_association: 

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