Feature Request: Add URLScan.io as Passive Subdomain Source

Description

Add URLScan.io as a new passive subdomain enumeration source for Subfinder.

Motivation

URLScan.io is a high-quality, reliable subdomain discovery service that provides real-time web scanning data. It has a generous free tier (1000 searches/day) and a well-documented API.

Benefits

• High-quality, actively maintained service
• Generous free tier: 1000 searches/day
• Well-documented REST API
• Real-time web scanning data
• Used by security researchers globally

API Details

• Endpoint: https://urlscan.io/api/v1/search/
• Rate Limit: 2 requests/second (free tier)
• Authentication: API key required
• Documentation: https://urlscan.io/docs/api/

Use Cases

• Discover subdomains from web scan archives
• Find recently active subdomains
• Complement existing sources like SecurityTrails, Shodan, etc.

Implementation

This feature has been implemented in a PR with proper rate limiting, API key authentication, and error handling.

Testing

Tested successfully with multiple domains:

• uber.com: 19 subdomains found
• example.com: 7 subdomains found

The source returns high-quality, verified results.