main.rb

require 'net/https'
require 'json'
require 'openssl'

=begin
UUID 			  = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
OS 				  = "<OS NAME> <VERSION> - <ARCH>"
USERNAME    = "YOUR USERNAME"
PASSWORD    = "YOUR PASSWORD"
TARGET_FONT = "jf-jinxuan-Medium"
=end

resp = Net::HTTP.post_form(
	URI("http://api.justfont.com/desktop/authdata"),
	u: USERNAME,
	p: PASSWORD
)

resp = JSON.parse(resp.body)

@user_id = resp['user_id']
@user_key = resp['user_key']

ts = Time.now.to_i

resp = Net::HTTP.post_form(
	URI("http://api.justfont.com/desktop/tokenget"),
	user_id: @user_id,
	auth: OpenSSL::HMAC.hexdigest('sha256', @user_key ,ts.to_s),
	uuid: 'uuid',
	os: 'osInfo',
	timestamp: ts
)

@token = JSON.parse(resp.body)['token']

resp = Net::HTTP.post_form(
	URI("http://api.justfont.com/desktop/userdata"),
	user_id: @user_id,
	token: @token,
	uuid: UUID,
	os: OS
)

resp = JSON.parse(resp.body)

@url = URI(resp['fonts'][TARGET_FONT]['url'])
@tmpfile = File.new(TARGET_FONT + ".tmp", "wb")

@tmpfile << Net::HTTP.get(@url)

@tmpfile.close

@tmpfile = File.new(TARGET_FONT + ".tmp", "rb")

cipher = OpenSSL::Cipher::AES256.new('CBC')
cipher.decrypt

@tmpfile.seek(-48,:END)

cipher.key = @tmpfile.read(32)
cipher.iv = @tmpfile.read(16)

@tmpfile.rewind

File.open(TARGET_FONT + ".otf", "wb") do |f|
	f << cipher.update(@tmpfile.read)
end

@tmpfile.close