Sliver proxy connection leak User-agent

[nikaiw]

Describe the bug
With default configuration, when a beacon connect through a proxy, sliver seems to leak it's user-agent. "Go-http-client"
To Reproduce
Steps to reproduce the behavior:
generate a beacon with proxy

Expected behavior
sliver use it's randomly generated user-agent
Screenshots

[alcastronic]

Can confirm this behavior. It uses the Go-Http-Client user agent in the Connect request.

$ python3 htt.py 
Server started http://xxx.xxx.xxx.xxx:3123

[+] CONNECT method called!
Host: api.example.com:443
User-Agent: Go-http-client/1.1


[+] POST method called!
Host: api.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36
Content-Length: 294
Upgrade-Insecure-Requests: 1
Accept-Encoding: gzip

[alcastronic]

This might be a solution, https://stackoverflow.com/questions/39577378/golang-net-http-transport-proxy-connect-method-header-supporting. Have not tested it yet, and I'm not really a go programmer, but it looks promising.