Using NKCSS.Antelope.Verify to validate clientside logins on the backend

Both MyCloudWallet and Anchor offer an option to, as part of the standard identity proof request, also sign a proof that you can individually validate on the backend. These proofs can be validated using ECDSA and are ideal for Unity/.NET backend applications and are invisible to the user, not requiring any additional actions compared to the normal client-side-only workflow.

How to enable this for MyCloudWallet

You can look here to see how you can make MyCloudWallet provide the additional proof, or check the NKCSS.Antelope.Verify for an example implementation.

How to enable this for Anchor

There isn't any documentation available that I could find, but it boils down to a proof property being available in the login response, which can be used to validte on the backend. It's signed with a 60-second expiration to prevent replay attacks. You can see an implementation example in the NKCSS.Antelope.Verify repository.