<p>Software-defined networking (SDN) is a pioneering paradigm that adds a new level of management and programmability to computer networks. Despite its benefits, SDN opens the door for new attacks against the network by targeting different SDN components, especially when they need to interact with each other through application programming interfaces (APIs). In this work, we focus on protecting those APIs by proposing SDN-API-Sec-Fast, a cross-domain access control method based on the key characteristics of blockchain technology. We enhance our previous work SDN-API-Sec by introducing SDN-API-Sec-Fast, which combines conflict detection with read-only mode to achieve better performance. We investigate the performance of the blockchain side and the overall authorization process.</p>