Describe the bug
The External host in the Forward auth of the Proxy Provider cannot save the non-standard port.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Providers‘
2. Click on 'Create'
3. Click on 'Proxy Provider'
4. Click on 'Forward auth(single application)'
5. Input 'https://startpage.example.com:4'
6. Click 'Finish'
7. See error 'Enter a valid URL.'

Expected behavior
All my services are accessed externally through specific ports, such as https://startpage.example.com:4. In Docker, port 4 is mapped to Traefik's port 443. Therefore, in my Proxy Provider's Forward Auth, the External host should be set to https://startpage.example.com:4

Version and Deployment (please complete the following information):

• authentik version: 2024.4.2
• Deployment: docker-compose