How to store received WebAuthn private key in Selenium tests (java)

Question

I am trying to build a selenium test (java) that goes through WebAuthn authentication. Thanks to thread here I am able to retrieve the private key. The question is how to store and reuse it? I tried to store private key to the disk

final PKCS8EncodedKeySpec privateKey = authenticator.getCredentials().get(0).getPrivateKey();
File outputFile = new File("./private.key");
Files.write(outputFile.toPath(), privateKey.getEncoded());

Then when I run test case for the same user I try to load it and create an instance of Credential like this:

Credential credential = Credential.createNonResidentCredential(
                id, "null", new PKCS8EncodedKeySpec(key), /*signCount=*/1);

and load the credentials to my driver:

VirtualAuthenticatorOptions options = new VirtualAuthenticatorOptions();
        options.setTransport(VirtualAuthenticatorOptions.Transport.INTERNAL)
                .setHasResidentKey(true)
                .setProtocol(VirtualAuthenticatorOptions.Protocol.CTAP2);
VirtualAuthenticator authenticator = ((HasVirtualAuthenticator) driver).addVirtualAuthenticator(options);
authenticator.addCredential(credential);

but the credential is got refused. Unfortunately I haven't found any information on how to transfer the credentials between the sessions. What is the usual workflow in this case? It should be quite common scenario I think