"known in advance" public key authentication?

[Ivan Shmakov]

        For my application, I need to establish a secure communication
        between two peers, and as it seems, TLS is a perfect fit for
        that.

        A feature of this application is that the public keys of the
        peers are effectively “known in advance”, so, while self-signed
        (unsigned?) X.509 certificates (or some OpenPGP ones) could be
        employed, there's no practical benefit from CC/WoT verification.

        Hence, the question is: is there a way to specify the local key
        pair and the remote public key to GnuTLS “directly”, just prior
        to connecting the remote?

        TIA.

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