In Chapter 9 of the O’Reilly ebook ‘Designing for the Internet of Things,’ Claire Rowland discusses the need for a cohesive user experience of a single application across such different devices:
In systems where functionality and interactions are distributed across more than one device, it’s not enough to design individual UIs in isolation. Designers need to create a coherent UX across all the devices with which the user interacts. That means thinking about how UIs work together to create a coherent understanding of the overall system, and how the user may move between using different devices.
HCI researchers coined the term ‘inter-usability’ to describe this sort of cross-device usability. The concept applies not only to how the user interacts with the application, but also how they interact with the identity management components securing that application – particularly mechanisms like consent and authentication. Just as critical as creating a coherent application UX is creating a coherent ‘Identity UX’ across devices.
For UX designers, dealing with multiple devices with different characteristics is a complication; for the purposes of authentication it presents an opportunity. The fact that devices differ in size, form factor, portability, user affinity, biometric capabilities, connectivity, etc. mean that we can tailor authentication models that leverage those differences.