Standard Notes authentication in ruby

auth.rb

resp = HTTP.use(:auto_inflate).get("#{BASE_URL}/auth/params?email=#{EMAIL}")
auth_params = JSON.parse(resp.body.to_s)

salt = Digest::SHA256.hexdigest([
  EMAIL,
  "SF",
  auth_params["version"],
  auth_params["pw_cost"],
  auth_params["pw_nonce"],
].join(":"))

pbk = PBKDF2.new(
  password: PASSWORD,
  salt: salt,
  iterations: auth_params["pw_cost"],
  hash_function: OpenSSL::Digest::SHA512,
  key_length: 768,
)
credentials = pbk.hex_string

split_length = credentials.length / 3
puts split_length

pw = credentials[0...split_length]
mk = credentials[split_length...split_length*2]
ak = credentials[split_length*2...split_length*3]

params = {email: EMAIL, password: pw}
resp = HTTP.use(:auto_inflate)
  .post("#{BASE_URL}/auth/sign_in", params: params)