In recent years, more and more Internet of Things (IoT) applications are emerging to make our daily life smarter. However, these IoT applications are developed in an isolated vertical architecture and suitable for a specific scene or environment. In other words, they do not exchange and reuse data between each other, resulting in the issue of IoT application isolations. To address this problem, we propose a cross-domain data sharing mechanism named MicrothingsChain, which allows the exchange and reuse of data among various applications in a collaborative way. This paradigm calls for novel security and access control mechanisms to enable resource-limited smart objects to verify a claimed access right without relying on central authorization systems. In this paper, we present a novel smart contract-based cross-domain authentication and access control mechanism for applicationcentric IoT. Specially, we propose a proof-of-edge computing node consensus protocol to avoid centralization in practice. The security analysis and experimental results demonstrate that MicrothingsChain is suitable for practice.