gistfile1.txt

def current_user=(val)
  session[:signed_token] = @user
  @user = User.find(....)
  @user.signing_token = session[:signed_token]
end


class User

#...

def signing_middleware
  (conn) -> {
    use :headers, 'X-Signing-Token' => self.signing_token
  }
end

def domains
  Account.middleware do |conn|
    self.signing_middleware.call(conn)
  end
  
  Account.find(account_ref: self.account_id)
end

end

gistfile2.txt

AssessmentScope.signing_token = -> { current_user.signing_token }