Message Filter Extension and domain alternate mode

The documentation (https://developer.apple.com/documentation/BundleResources/Entitlements/com.apple.developer.associated-domains)

for a message filter extension says:

If you use a private web server, which is unreachable from the public internet, while developing your app, enable the alternate mode feature to bypass the CDN and connect directly to your server.

<service>:<fully qualified domain>?mode=<alternate mode>
Where alternate mode is one of the following:
developer
Specifies that only devices in developer mode can access the domain. In this mode, you can use any valid SSL certificate on your web server, including a certificate that the system doesn’t trust. 

What does it mean "you can use any valid SSL certificate on your web server"?

Does the app have to do anything with regards to this?

The server that your Message Filter Extension interacts with can be tested privately using SSL on your server to communicate with the extension. There isn't much to do on the app side relating to this, as it is mostly for your backend.

Thanks.

It says only devices in developer mode can access the domain. To clarify that means any iPhone can be used, provided developer mode is enabled in Settings. The phone doesn't been to additionally be registered with the developer account?

Message Filter Extension and domain alternate mode
 
 
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