How to configure multi realm in nestjs nest-keycloak-connect library?

Question

They ask to pass this configuration, but it doesn't explain how it works, and since I use token from 2 different realms I can't authenticate. Can someone explain to me how to do all the configuration

    authServerUrl: 'http://localhost:8180/auth',
      clientId: 'nest-api',
      secret: 'fallback', 
      returns null
      multiTenant: {
        realmResolver: (request) => {
          return request.get('host').split('.')[0];
        },
        realmSecretResolver: (realm) => {
          const secrets = { master: 'secret', slave: 'password' };
          return secrets[realm];
        }
      }
    }