How to calculate PRF in OpenSSL?

I'm developing a EAP-TLS server using OpenSSL. I need to derive key material from TLS session as described in RFC5216.

Key_Material = TLS-PRF-128(master_secret, 开发者_Go百科"client EAP encryption", client.random || server.random)

I can get master secret in TLS connection by visit SSL_SESSION->master_key, but how could I calculate PRF by OpenSSL?

---

I just get the answer from the OpenSSL user mailing list. There is a patch to OpenSSL recently. you can find it on this link sctp.fh-muenster.de/dtls/tls-exporter.patch . People have the same question as me can refer to the patch's implementation.