public static byte[] exportKeyingMaterial(SSLSocket socket, String label, byte[] context,
            int length) throws SSLException {
        return toConscrypt(socket).exportKeyingMaterial(label, context, length);
    }
Exports a value derived from the TLS master secret as described in RFC 5705.

@param label the label to use in calculating the exported value.  This must be
an ASCII-only string.
@param context the application-specific context value to use in calculating the
exported value.  This may be {@code null} to use no application context, which is
treated differently than an empty byte array.
@param length the number of bytes of keying material to return.
@return a value of the specified length, or {@code null} if the handshake has not yet
completed or the connection has been closed.
@throws SSLException if the value could not be exported.
common/src/main/java/org/conscrypt/Conscrypt.java