[AVM Module Issue]: Authentication (Easy auth) secret on the app settings

@pankajagrawal16 is already working on this.

Since Sep 3, 2025.

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Issue Type?

I'm not sure

### Module Name

avm/res/web/site

### (Optional) Module Version

0.11.1

### Description

Hi!

I am using the site module and trying to add the client secret of the app to the app settings (environment variables) since I want to use the built-in Azure authentication middleware.
I tried to pass the `EASYAUTH_SECRET` in to the appsettings object as in the [example](https://github.com/Azure/bicep-registry-modules/tree/main/avm/res/web/site#example-2-function-app-using-large-parameter-set) . This works fine when I have a hardcoded secret but if I am going to follow security best practices I will need to have it in a more secure place like a Keyvault. The `.getSecret('secretName')` method of the Keyvault is allowed only for passing the value to a module parameter that has the `@secure()` decorator.

Example:
```
module app 'br/public:avm/res/web/site:0.11.1' = {
name: 'app'
params: {
appSettingsKeyValuePairs: {
EASYAUTH_SECRET : existingKeyvault.getSecret('MyAppClientSecret')
}
...
```

Is there a "secure" way to pass in the Easy auth secret to the app settings using the verified module?

I am trying to resolve this now by manually appending the appsettings with a custom module where I unify existing appsettings with the secret but I would like to be able to send this value in the verified module directly instead, especially when the example states that this should be a possible configuration.

Appreciate any responses.

### (Optional) Correlation Id

_No response_