[BUG]: DevProxy interferes with other apps which urls aren't watched

[ThaDaVos]

Description

Currently when I enable DevProxy (as I need it for development) - some other apps, like the New Outlook and Whatsapp Desktop Client - stop functioning, like they don't seem to have internet access anymore until I stop the DevProxy and sometimes have to restart the app first, especially Whatsapp.

Expected behaviour

No interference with other apps which URLs aren't watched

Actual behaviour

Interference with other apps which URLs aren't watched

Steps to reproduce

Below happens instantly after starting the proxy, but sometimes after a little while - it's flakey buy always happens eventually

Outlook (using an Microsoft Exchange Online account, don't know if this is important)

1. Open Outlook
2. Start DevProxy
3. Send yourself an email from your phone - or even from Outlook (won't send)
4. It never shows up in Outlook as it lost internet access - same goes for trying to open an email which you haven't opened yet, or when trying to search

Whatsapp

1. Open Whatsapp
2. Start DevProxy
3. Try to send or download a file - messages seem to go through but not always

Dev Proxy Version

0.28.0

Operating system (environment)

Windows

Shell

PowerShell

Configuration file

{
	"$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v0.28.0/rc.schema.json",
	"plugins": [
		{
			"name": "DevToolsPlugin",
			"enabled": true,
			"pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll"
		}
	],
	"urlsToWatch": [
		"https://b2bapi.snelstart.nl/*",
		"https://auth.snelstart.nl/*"
	],
	"logLevel": "information",
	"newVersionNotification": "stable",
	"showSkipMessages": true
}

Additional Info

No response

[waldekmastykarz]

Thanks for reporting the issue and sorry for the trouble @ThaDaVos. Have you by any chance seen a similar issue with other proxies such as Fiddler? I wonder if what you're seeing could be caused by certificate pinning or something similar. Even though Dev Proxy is not decrypting these URLs, it's still present in the request pipeline.

As a possible workaround you could consider:

1. If you know URLs used by other apps, exclude them from going through a proxy altogether. You can do this from Settings > Network & Internet > Proxy > Use the proxy server except for addresses that start with the following entries.
2. Don't register Dev Proxy as a system proxy (--as-system-proxy false in command line or "asSystemProxy": false in devproxyrc.json) and explicitly send your application traffic to Dev Proxy (eg. by setting the https_proxy env var for your application)

I hope this helps.