I am in the process of implementing Single Sign-On (SSO) across multiple sites and am intending on introducing a shared header. Two of the sites follow the same 'main site' navigation where as others have their own navigation system. 

I was planning on having all the sites featured in the top with the current site being highlighted. However, I have been told this is bad practice because there will be two links to the same site every time in one instance. Additionally a concern has been raised about the scalability of this - ways to introduce new sites without limited header space. 

In the long term I know navigational work needs to be done to bring the sites together, in the short term **is it bad practice to have some duplication with one link at a time to bring the sites together?** 

The alternative would be to leave out the navigational element and have login / view profile & logout only.