We do not have much documentation on this, because XAF has not been designed for such scenarios. While it is technically possible to implement certain multi-tenant features with XAF (for instance, check out How to implement company-level filtering in a multi-tenant scenario, How to change connection to the database at runtime, etc.), performance questions immediately arise. Such Web apps usually assume a high load (thousands of users) and a product that costs two thousand bucks (XAF Web UI) would not be a good fit for this. Solutions of such a scale imply different software architectures and budgets too.
Aside from performance, we have not done any special optimizations for SaaS feature-wise in the last 10+ years of XAF existence. As a result, the usability of the aforementioned existing solutions may be improved or they may have limitations. XAF customers who have been using XAF in multi-tenant or SaaS scenarios with few concurrent users are rather the exceptions than the rule. You can learn more about our position from XAF Web UI for SaaS with 1000 users, Looking to start developing a SaaS multi tenant application. and other tickets in our support knowledge base: one, two.
Let me know if you have any questions or if I misunderstood your requirements.