Intergrate WAF with ElasticBeanstalk's ALB using CloudFromation

Question

I have create a WAF and an Elastic Beanstalk with ALB like this:

TestTemplate:
    Type: 'AWS::ElasticBeanstalk::ConfigurationTemplate'
    Properties: 
      ApplicationName: !Ref TestApplication
      Description: Test
      SolutionStackName: '64bit Amazon Linux 2 v3.5.7 running PHP 8.1'
      OptionSettings:
        ...
        # Environment
        - Namespace: aws:elbv2:loadbalancer
          OptionName: SecurityGroups
          Value: !Ref TravelManagerPrdElbEnv

The WAF snippet and EB are all in a same stack. How do I integrate the WAF with ALB of the EB ? I know there is this "WebACLAssociation" but in this case, I do not know how to get ALB's ARN .. Please help