The ES docs for FIPS 140.2 compliance refers to making changes to the hashing methods. Those docs state.
You must set the cache.hash_algo realm settings and the xpack.security.authc.password_hashing.algorithm setting to one of the PBKDF2 values.
I can see where to put the xpack.security.authc.password_hashing value - but I cannot locate any docs on the cache.hash_algo realm setting. Any idea?