Scientific workflows have become an important instrument for domain scientists to synergistically integrate distributed computations and data to accelerate scientific discoveries. Existing scientific workflow tools, however, only support single scientists to compose scientific workflows in a desktop application. Nowadays, many scientific research projects are becoming increasingly larger scale, requiring that multiple research partners with different expertise collaborate from distributed organizations. Therefore, there is a critical need of a collaborative scientific workflow tool that supports domain scientists to cooperatively design, compose, annotate, execute, monitor, and manage scientific workflows over the Internet in both synchronous and asynchronous modes. This research reports the design and development of our preliminary version of a collaborative scientific workflow tool based on an open-source, single-user tool Taverna. We present our study of the role-organization-based access control technique over collaborative scientific workflow composition.