DX: Improve HTTP request accessor

[ArthurHoaro]

Follow-up of #1972 (review)

With the latest upgrade to Slim 4, we retrieve query and payload parameters, with $object->getArray()['key'] ?? 'default'.
This is not great for readability and maintainability, and could easily be improved with either:

• a simple helper function
• a wrapper around requests object

Whichever solution can make the code better and is relatively easy to set up.