@user = {
    :user => {
        :id => 'johndoe', # required
        :displayname => 'John Doe', # required
        :email => 'john.doe@gmail.com',
        :avatar => '//gravatar.com/avatar/e5fb96fe7ec4ac3d4fa675422f8d1fb9',
        :is_admin => true
    }
}
require 'digest/sha1'
require 'base64'
require 'json'
 
# timestamp (in seconds). Improves security.
@timestamp = Time.now.to_i
 
# Message (base64 encoded string)
@message = Base64.strict_encode64 @user.to_json
 
# Signature (signed with private key)
@signature = Digest::SHA1.hexdigest "ocUxp5e20qOb7hP5Dm7j5emH #{@message} #{@timestamp}"