Gets a pointer to the User Key Material to be used as part of the selected
Key Derivation Function associated with the given key exchange ctx.
-=item "kdf-ukm-len" (B<OSSL_EXCHANGE_PARAM_KDF_UKM_LEN>) <size_t>
-
-Gets the size of the User Key Material to be used as part of the selected
-Key Derivation Function associated with the given key exchange ctx.
-
=back
=head1 EXAMPLES