Hi @kathir, welcome to the community! it’s hard to say without knowing exactly what applications and environment you are working with. Since you mention both internal and external apps, some good solutions to look at may be Duo Single Sign-On, or perhaps the Duo Web SDK.
The best people to answer your question though would be the Duo Sales team. You can share more about your use case with them, and they’ll recommend the ideal solution based on those details 
Use the Contact page here for more info.
