Thank you for your patience while I worked on your query and apologize for the delay in our response.
We can get the token to use managed identity for load test, but there is no way to get inside the azure load test. App Service and Azure Functions provide an internally accessible REST endpoint for token retrieval.
For your reference: Load test authenticated endpoints | Microsoft Learn
Hope this helps. Do let us know if you any further queries.
Thanks,
Navya.