Universal Containers wants to use an external Web Service provided by a third-party vendor to validate that shipping and billing addresses are correct. The current vendor uses basic password…

Universal Containers wants to use an external Web Service provided by a third-party vendor to validate that shipping and billing addresses are correct. The current vendor uses basic password authentication, but Universal Containers might switch to a different vendor who uses OAuth. What would allow Universal Containers to switch vendors without updating the code to handle authentication?