Gen oct key from a secret

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Hi,
First of all, very good job.
I'm looking for to generate an oct key from a password or a secret (string). To explain it a little more :
The goal is to exchange encrypted data between the client and the server (PHP/JAVA/nodeJS/...) in a JWE format.
At first, the client send the password to the server using the public RSA/ECC key of it -> JWE.
The server respond to the client in JWE format too, but using the password to generate a oct key to encrypt.
Le client read the JWE by generating an oct key from the password and the alg of the header of the JWE.

I didn't see in the examples the possibility to do that. Is there a way ?

Thank you for the answer.