Our legacy applications store user account information in a database. I can't seem to find clear information as to whether AD FS 3.0 supports authentication against both Active Directory as well as SQL Server.
To be clear about my question:
How can AD FS 3.0 be used to provide federated authentication for users stored in both SQL Server (if at all) as well as Active Directory?
TIA
In short, it can't.
ADFS 3.0 and below can only authenticate against AD. It can, however, use a SQL Server DB for authorization i.e. it can query the DB for attributes that it uses to build up claims.
Have a look at Identity Server which authenticates against SQL Server. You can federate this with ADFS.
ADFS 4.0 (Server 2016) will be able to do this i.e. AD / LDAP for authentication.