Sign a data using a certificate in pfx

Question

I have a pfx file of my electronic digital signature, located in assets. I need to sign random data in base64 using this certificate and get a signed string in base64 at the output. I am developing the application on flutter windows. I tried to find libraries, but they are only for flutter android. This is my first experience working with a pfx file via dart. Please, the simplest example will solve my problem.

I tried to use ffi with c++, but the task is to write an application in pure dart without using ffi.