How to use rawr-x3dh without private keys?

[PoCk3T]

First of all, thank you @soatok for creating such a library

Would you and/or any kind member of the community points me towards the right direction for a small project I'm working on?

Scenario: a frontend leveraging rawr-x3dh has access to the public key of a user, can ask the user to sign a message with their private key, but doesn't have access to the private key itself.

Question: would it still be possible to leverage rawr-x3dh one way or another, even if deriving an alternative private key out of signed message?

More context/researches done so far:

• I was originally checking the unit tests as part of the code base of this project, but I see that the keys are derived out of a key pair that was created locally, with full access to the private key:

  rawr-x3dh/tests/x3dh.test.ts

  Line 24 in c783ef7

  const fox_keypair = await sodium.crypto_sign_keypair();

  which is a luxury I unfortunately don't have :)

Thank you in advance to any one who can share any insights/tips 🥇