We're looking to use Azure Active Directory as our user store for an external-facing application. Currently, our MVC/C# 4.5 app (using WIF) is authenticating against an on-premise ADFS 2.0 proxy/server via passive federation and we'd like to "port" this up to Azure. The way we're going about this, we're having ACS sit between AAD and our application such that ACS is replacing ADFS and AAD is replacing Active Directory (on prem).
From a technical standpoint, we have this working. However, we have a major problem in that users must login with not just their username but also the domain name. It's unreasonable (and simply a deal-breaker) to force a fictitious email address on our users as their username.
Is there some way to set this up such that the user need not type in a domain name? In our case, we have only one Identifying Party behind ACS: the one AAD directory. So we always know in advance what the domain name should be.
Thanks in advance!