Gets a bearer token (default) or stream token based on tokenType parameter.

For Bearer Tokens (tokenType=bearer or omitted):
Send grant in request body with supported grant types:

• grant_type=password - Username/password authentication
• grant_type=refresh_token - Refresh token flow
• grant_type=auth0_token - Auth0 SSO authentication

For Stream Tokens (tokenType=stream):
Generates a short-lived JWT token for call recording downloads.
Provide authentication via:

1. Bearer token in Authorization: Bearer {token} header (body can be empty), OR
2. auth0_token={token} in request body