@Andres.Aulasneo @Alecar thanks for your likes 
@Alecar as you say, you have to configure SESSION_COOKIE_DOMAIN in site values, overwriting the default value and assigning the same value as site domain’s name, but I think this is not due to the changes introduced in the PR.
Regarding to the frontend part, we are planning to address this part by deploying as many copies of MFEs as sites, each one properly configured to the corresponding domain. Since we host MFEs in S3 it will not add an extra cost in infrastructure, but it does force us to do a new deployment every time we create a site. @dcoa with your proposal we can avoid this drawback, how did you plan to implement this part?