I have a pretty good job. My work is stimulating, there is a strong career path, and clear room for advancement. I'm not actively looking for a new job.
However, I also frequently receive inquiries from former bosses, supervisors, and coworkers asking me if I am interested in opportunities at their companies. Occasionally (maybe 1-2 a year) someone does mention something interesting, and I apply.
I am concerned about handling references with these jobs. My professional references are generally supervisors or managers of past/current projects. In an active search, I would talk to them about my intentions and ask them to be a reference. That seems a bit strong for my situation: I am not actively seeking. I don't want to alarm people by making them think I am unsatisfied or preparing to leave.
What is the best way to handle asking for references in this kind of situation?