Need Custom Public IP Provider Over VPN #603

Has this issue been covered in the Wiki?

• I have read the Wiki and my issue is not covered.

Is there an existing issue reported already?

• I have searched the existing issues, it does not exist.

Describe the new feature you would like

Need to support custom public IP check providers, as proxy clients (such as sing-box, Clash, or Xray) route domestic (mainland China) and overseas traffic differently based on GeoIP, causing the IP check to display an incorrect result.