  The ongoing transformation of mobile networks from proprietary physical
network boxes to virtualized functions and deployment models has led to more
scalable and flexible network architectures capable of adapting to specific use
cases. As an enabler of this movement, the OpenRAN initiative promotes
standardization allowing for a vendor-neutral radio access network with open
APIs. Moreover, the O-RAN Alliance has begun specification efforts conforming
to OpenRAN's definitions. This includes the near-real-time RAN Intelligent
Controller (RIC) overseeing a group of extensible applications (xApps). The use
of these potentially untrusted third-party applications introduces a new attack
surface to the mobile network plane with fundamental security and system design
requirements that are yet to be addressed. To secure the 5G O-RAN xApp model,
we introduce the xApp Repository Function (XRF) framework, which implements
scalable authentication, authorization, and discovery for xApps. We first
present the framework's system design and implementation details, followed by
operational benchmarks in a production-grade containerized environment. The
evaluation results, centered on active processing and operation times, show
that our proposed framework can scale efficiently in a multi-threaded
Kubernetes microservice environment and support a large number of clients with
minimal overhead.
