I get a warning that HMAC_CTX_new(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and HMAC_CTX_free() are deprecated.
Is there a new way to implement hmac_sha256() function?

For many years now MD5 has been on course for being phased out of a lot of different projects, tools, and libraries. There are many alternatives to MD5 that are being used nowadays, but one of the reasons it has continued to be available for such a long time is that MD5 is still being used quite a bit (including with modern eMail authentication protocols such as CRAM-MD5 and DIGEST-MD5 which are commonly supported for SMTP authentication).