Application navigation when there are multiple main navigation possibilities?

What's the best way to present main navigation for a site where you login and have access to two products, that have some different navigation.

3 navigations: 1) External page, about us, products etc.. -- Login In ---- 2) Product 1 navigation... clients, service, product-1 specific link 1, P1-SL 2 3) Product 2 navigation... clients, service, product-2 specific link 1, P2-SL 2

Some users may only have access to product 1, some only product 2, some both 1 & 2.

Separate sub-dashboards or views? two rows? I think blending all the navigation for product 1 and 2 (and eventually 3,4) will get too long.
Solution should be mobile/responsive friendly.