VS 2019 Sign data with private key in .key file

Hello,

I have two files in PEM format
- Certificate file (.crt): -----BEGIN CERTIFICATE----- ...-----END CERTIFICATE-----
- Private key file (.key): -----BEGIN PRIVATE KEY-----...-----END PRIVATE KEY-----

I'm looking for the best way of signing with the private key a randomly generated base-64 encoded string of at least 100 bytes

Any guidance or feedback is more than welcome.

Thanks!