Feature Enhancement: Extend GitHub OAuth to Support GitHub Enterprise

This feature enhancement extends the GithubOAuthProvider class to support GitHub Enterprise environments, allowing for greater flexibility and integration with custom GitHub domains.

This is the implementation for the feature request I created yesterday: #1484

Key Changes:

• Custom GitHub Domain Support:
  • Added new environment variables, OAUTH_GITHUB_CUSTOM_URL and OAUTH_GITHUB_CUSTOM_API_URL, enabling the setup of a custom GitHub domain and API. If not specified, This defaults to github.com if not specified.
• API URL Customization:
  • The API URL is now dynamically constructed using the custom domain, ensuring compatibility with GitHub Enterprise instances.

Benefits:

• Enterprise Compatibility:
  • Users can now seamlessly integrate with GitHub Enterprise, utilizing their specific domain configurations.
• Backward Compatibility:
  • Maintains existing functionality for standard GitHub users by defaulting to the public GitHub domain and API URL.
• Enhanced Flexibility:
  • Provides a more adaptable OAuth solution for diverse GitHub environments.

Please review the changes and provide feedback or approval. Let me know if there are any questions or further adjustments needed.