Hello,
I have recently uploaded a workflow to the KNIME Hub, which you might find useful (or most probably not yet as it is quite basic still). It parses the configured OpenAPI REST API contract (as a JSON) and generates helper components based on them to make calling them easier. (The URLs’ query parameters and path parameters can be used from the input table if they follow the input_{{type}}_{{name}} format.)
Probably it contains a lot of errors, it might be non-optimal in many places. 
It was saved with KNIME 5.4.3, so you probably need a recent KNIME to open it.
I appreciate any feedback, questions, contributions.