[Python] Is this Python code performing SHA512 or a variant of SHA512?

I'm trying to convert this Python to C++:

import base64
from cryptography.hazmat.primitives.serialization import load_pem_private_key


with open(PRIVATE_KEY_PATH, 'rb') as f:
private_key = load_pem_private_key(data=f.read(),
password=None)

data = "test"

signature = base64.b64encode(private_key.sign(data.encode('ASCII')))


I think it's performing SHA512?

However, when I look for C/C++ implementations performing SHA512 they seem to all accept only one argument, whereas this has two: data and key.

What is this doing exactly? Is it something like a HMAC-SHA512?

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