What would you like to see added?

Configurable usage of picojson and nlohmann json

Additional Context

Hello,

Would it be possible to make usage of the two json external libraries optional by a CMake flag / config ?

I am using jwt-cpp as a FetchContent dependency in my project and also using myself nlohmann/json (a newer version) as a direct dependency. Hence I run into issues when I am including nlohmann/json.hpp, as it violates the ODR with two files in parts of the project.

If I have the time, I will work on a PR to solve this dependency issues.
Thanks