HMAC something in Ruby/Rails

hmac_example.rb

# ruby 2.5.0, rails 5.1.4

key = SecureRandom.hex(32) # Need 256 bits = 32 bytes of entropy. Since in hex it will be 64 characters long.
data = 'example data that I want to hmac could be json string of a big Hash for example'

hmac_bytes = OpenSSL::HMAC.digest(OpenSSL::Digest.new('sha256'), key, data) # raw bytes (in string representation)
hmac_base64 = Base64.urlsafe_encode64(hmac_bytes) # often sending in a link so I use urlsafe version