# frozen_string_literal: true

module EE
  module KerberosSpnegoHelper
    extend ::Gitlab::Utils::Override
    include ActionController::HttpAuthentication::Basic

    attr_reader :spnego_response_token

    override :allow_basic_auth?
    def allow_basic_auth?
      if ::Gitlab.config.kerberos.enabled && ::Gitlab.config.kerberos.use_dedicated_port
        !request_uses_kerberos_dedicated_port?
      else
        true
      end
    end

    override :allow_kerberos_spnego_auth?
    def allow_kerberos_spnego_auth?
      return false unless ::Gitlab.config.kerberos.enabled

      if ::Gitlab.config.kerberos.use_dedicated_port
        request_uses_kerberos_dedicated_port?
      else
        true
      end
    end

    def request_uses_kerberos_dedicated_port?
      request.env['SERVER_PORT'] == ::Gitlab.config.kerberos.port.to_s
    end

    def spnego_challenge
      if spnego_response_token
        "Negotiate #{::Base64.strict_encode64(spnego_response_token)}"
      else
        'Negotiate'
      end
    end

    def spnego_provided?
      request.authorization.present? && (auth_scheme(request) == 'Negotiate')
    end

    def send_final_spnego_response
      headers['Www-Authenticate'] = spnego_challenge if spnego_response_token
    end

    # rubocop: disable CodeReuse/ActiveRecord
    def find_kerberos_user
      krb_principal = spnego_credentials!(spnego_token)
      return unless krb_principal

      identity = ::Identity.with_extern_uid(:kerberos, krb_principal).take
      identity&.user
    end
    # rubocop: enable CodeReuse/ActiveRecord

    # The Kerberos backend will translate spnego_token into a Kerberos
    # principal and/or provide a value for @spnego_response_token.
    def spnego_credentials!(spnego_token)
      require 'gssapi'
      gss = GSSAPI::Simple.new(nil, nil, ::Gitlab.config.kerberos.keytab)
      # the GSSAPI::Simple constructor transforms a nil service name into a default value, so
      # pass service name to acquire_credentials explicitly to support the special meaning of nil
      gss_service_name =
        if ::Gitlab.config.kerberos.service_principal_name.present?
          gss.import_name(::Gitlab.config.kerberos.service_principal_name)
        else
          nil # accept any valid service principal name from keytab
        end

      gss.acquire_credentials(gss_service_name) # grab credentials from keytab

      # Decode token
      gss_result = gss.accept_context(spnego_token)

      # gss_result will be 'true' if nothing has to be returned to the client
      @spnego_response_token = gss_result if gss_result && gss_result != true

      # Return user principal name if authentication succeeded
      gss.display_name
    rescue GSSAPI::GssApiError => ex
      Rails.logger.error "#{self.class.name}: failed to process Negotiate/Kerberos authentication: #{ex.message}"
      false
    end

    def spnego_token
      Base64.strict_decode64(auth_param(request))
    end
  end
end
