Exchange an API key and client secret for a bearer access token used on /api endpoints.

Quickstart:

1. Generate credentials from POST /account/api-access/credentials/rotate.
2. Call this endpoint with x-api-key and x-client-secret.
3. Use the returned token on all /api requests:
   Authorization: Bearer <access_token>

Example:

curl -X POST "$BASE_URL/account/api-access/token" \
  -H "x-api-key: <api_key>" \
  -H "x-client-secret: <client_secret>"