[FEATURE REQ] OpenAPI specification for Foundry Tools token exchange (issueToken)

### API Spec link

N/A

### API Spec version

N/A

### Please describe the feature.

Foundry Tools has an "[Authenticate with an access token](https://learn.microsoft.com/en-us/azure/ai-services/authentication#authenticate-with-an-access-token)" workflow, involving exchanging a subscription key for a temporary access token.

I am requesting an OpenAPI specification for this endpoint.

Start by reviewing the linked Microsoft authentication workflow and the issueToken token-exchange endpoint described in the request. Done means adding an OpenAPI specification that accurately documents exchanging a subscription key for a temporary access token; the request provides no API spec link or version, so its contract must be established first.

Written by the indexing model from the issue text.