UCWA 1.0 reference
Microsoft Unified Communications Web API 1.0 is a REST API that exposes Lync Server 2013 instant messaging (IM) and presence capabilities.
UCWA 1.0 enables developers to make their enterprise applications and intranets more lively and connected to business contacts.
Key use cases enabled by this API include:
Lighting up Lync presence in business apps and intranets.
Embedding IM experience in enterprise-specific Line of Business apps across platforms/browsers/devices (contextual communications), especially Windows 8, Apple iPad, and others.
Enabling Web Chat - pro-active chat feature for e-commerce site, helpdesk, support, and other scenarios.
UCWA 1.0 is available only to customers who have Lync on-premises.