Convert string to sha256 / base64

Hello,
We work in collaboration with a company that develops in .NET. We need to ask one of their web services. We need to convert a querystring to sha256 and convert the base64 result to string.
The concern is that we work on the unix side, and that we cannot (client constraint) install core.net. We are looking for an alternative to do what is done in .NET on the openedge side. Do you have any leads for me?

We wanted to find the equivalent in shell, but we don't come across the same result, I think the .NET functions do other things.

Thank you