After installing espressif32_stage (because the fairly new HTTPClient library was missing), HTTPClient now throws the following compile error:
/Users/sijmen/.platformio/packages/framework-arduinoespressif32 @src-537c58760dafe7fcc8a1d9bbcf00b6f6/libraries/HTTPClient/ src/HTTPClient.cpp:30:30: fatal error: WiFiClientSecure.h: No such file or directory
Why this happens is beyond me as WiFiClientSecure is, just like HTTPClient, an included library and has been that way for six months (according to the git history).
[env:esp32] platform = espressif32_stage framework = arduino board = nodemcu-32s lib_deps = ArduinoJson DHT sensor library
A workaround for this is symlinking the header files in the WiFiClientSecure folder to the HTTPClient folder in the platform directory. It looks like there’s a problem with built-in libraries depending on other built-in libraries.