[Bicep/ARM] Cannot set custom domain

**Describe the bug**

I'm trying to create a SWA from scratch using Bicep, and setting custom domains the same way.

My template looks like this for the SWA part:

```bicep
resource staticWebApp 'Microsoft.Web/staticSites@2021-01-15' = {
name: '${appName}-staticwebapp${dashSuffix}'
location: location
sku: {
name: 'Standard'
tier: 'Standard'
}
properties: {
repositoryUrl: 'https://github.com/${githubRepo}'
branch: 'main'
provider: 'GitHub'
repositoryToken: githubToken
buildProperties: {
appLocation: '/'
apiLocation: ''
outputLocation: 'dist/${projectName}'
skipGithubActionWorkflowGeneration: true
githubActionSecretNameOverride: 'AZURE_SWA_TOKEN'
}
stagingEnvironmentPolicy: 'Enabled'
allowConfigFileUpdates: true
userProvidedFunctionApps: [
{
functionAppResourceId: functionApp.id
functionAppRegion: location
}
]
}
dependsOn: [
functionApp
]

resource staticWebAppDomains 'customDomains@2021-01-15' = [for domain in domains: {
name: domain
properties: {
validationMethod: 'dns-txt-token'
}
}]
}
```

I would like to use TXT validation for validating the domain names, as seen here in the template.
I have 2 issues doing that:

- I don't know how to get the generated token code, so I can put in the Azure DNS template. I found nothing related in the docs.

- The Bicep template without the `customDomains` part works fine. But when I add the `customDomains` section, it never returns and seems to get stuck (waiting for the validation to succeed?). When I break out of the deployment (with CRTL+C) as it's waiting forever, get an error when I'm trying to redeploy because the previous deployment never ended:
```
{"error":{"code":"DeploymentActive","message":"Unable to edit or replace deployment 'poc': previous deployment from '10/12/2021 12:33:34 PM' is still active (expiration time is '10/19/2021 12:28:14 PM'). Please see https://aka.ms/arm-deploy for usage details."}}
```
I have to cancel the deployment manually otherwise it gets stuck for days.

Note that I'm deploying the bicep template with `az deployment group create`.

**Expected behavior**

Adding `customDomains` resources to my SWA Bicep template should work without getting stuck in the process, and I should be able to retrieve the generated validation codes to use then in the Azure DNS part of the Bicep template.

**Additional info:**

I should mention that the custom domain are correctly set, as I can see them in the Azure portal, in the custom domains section of the deployed SWA, waiting on "validating" message.