In a 3rd step, the proxy asks the API for C. The API checks if B has the rights to make use of C after which you can forwards C towards the proxy.
IBM has used the Linux Foundation Open Source Summit today to announce https://cyrusnequ830231.thenerdsblog.com/36298904/data-loss-prevention-confidential-computing-tee-confidential-computing-enclave-safe-ai-act-confidential-ai-data-security-data-confidentiality-an-overview