When trying to use the HS512256 algorithm I'm seeing Unsupported digest algorithm (sha512256).: first num too large. I've narrowed this down to the OpenSSL::Digest.new("sha512256") call in https://github.com/jwt/ruby-jwt/blob/master/lib/jwt/algos/hmac.rb#L14

irb(main):001:0> require 'openssl'
=> true
irb(main):002:0> "HS512256".sub('HS', 'sha')
=> "sha512256"
irb(main):003:0> OpenSSL::Digest.new("sha512256")
Traceback (most recent call last):
        6: from /usr/local/bin/irb:23:in `<main>'
        5: from /usr/local/bin/irb:23:in `load'
        4: from /usr/local/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        3: from (irb):3
        2: from (irb):3:in `new'
        1: from (irb):3:in `initialize'
RuntimeError (Unsupported digest algorithm (sha512256).: first num too large)

The ruby:2.6 container has the latest released OpenSSL gem per https://github.com/ruby/openssl/releases

$ docker run --rm -ti ruby:2.6 gem list openssl

*** LOCAL GEMS ***

openssl (default: 2.1.2)

I also don't see this algorithm in https://ruby-doc.org/stdlib-2.6/libdoc/openssl/rdoc/OpenSSL/Digest.html. Is SHA512256 correct?