In your Fluently.Config(), the section Mappings(m -> m..., you need to tell FluentNhibernate to include the mappings in the package, like so:
.Mappings(m =>
m.FluentMappings
.AddFromAssemblyOf<UserAuthPersistenceDto>())
Yours should probably end up looking something like
.Mappings(m =>
{
m.AutoMappings.Add(mapping);
m.FluentMappings
.AddFromAssemblyOf<UserAuthPersistenceDto>();
})