With this small program the Account-ID of a user can be queried.
Just download the zip file, extract it and execute the PlayStationSharp.TestApp.exe file.
You need to perform a PSN login to get the proper credentials in order to perform the PSN queries.
The source code of the program can be found here.
If you don't trust this program download the project and compile and build it yourself :)
Note:
- In order to be able to run this program you must have installed .NET framework 4.7.2 on your PC