Microsoft.Web/sites@2015-08-01: The property "identity" does not exist in the resource or type definition, although it might still be valid

### Resource Type

Microsoft.Web/sites

### Api Version

2015-08-01

### Issue Type

Missing property(s)

### Other Notes

_No response_

### Bicep Repro

resource idsWebApp 'Microsoft.Web/sites@2015-08-01' existing = {
name: ''
}

output principleId string = idsWebApp.identity.principalId

### Confirm

- [X] I have read the troubleshooting guide and looked for duplicates.

Start with the Microsoft.Web/sites type definition for API version 2015-08-01 and reproduce the Bicep example that reads identity.principalId. Compare the resource's supported identity shape with the definition; done means the shown output is accepted without the missing-property diagnostic.

Written by the indexing model from the issue text.