Improving Authentication Configuration for Enterprise Use

[mrjasonroy]

The current authentication setup has several limitations that make enterprise deployment challenging:

• Social login buttons appear even when providers aren't configured
• Can't disable email/password auth for social-only deployments
• No Microsoft/Azure AD support (critical for enterprises)
• Auth config exposed via NEXT_PUBLIC_* variables
• No runtime validation or CORS configuration
• UI doesn't scale well for multiple providers

Proposed Solution

Create a centralized, validated authentication configuration system:

• Zod-validated config with runtime checking
• Dynamic provider display based on actual configuration
• Microsoft auth support with tenant configuration
• CORS support via ALLOWED_ORIGINS
• Flexible auth controls (EMAIL_AND_PASSWORD_ENABLED, SIGN_UP_ENABLED)
• Improved UI that scales for multiple providers

I've already implemented this with comprehensive tests. Would love feedback before submitting a PR!

[mrjasonroy]

The PR related to this feature is here - #211