Hi Nick,
Currently the MP Builder only supports JSON responses -- there's no workaround to use an unformatted response directly. A couple other options to explore as workarounds:
1. The TrendMicro Deep Security API may support Basic Auth rather than using a session token.
2. If the session token doesn't expire (or has a sufficiently long expiration), you could manually generate a token one time and set the session token header in Custom authentication (step 2 of Source configuration). If you do this, it is recommended to select 'sensitive' for the API token header.
Please let me know if either of these approaches will work for you, or if you need any further assistance.
Best regards,
Mark