Gov. Charlie Baker on Wednesday said a vaccine passport app may "soon" be available to vaccinated residents in Massachusetts and other states who want to show proof of vaccination against COVID-19.

Baker made the comment while appearing on GBH's Boston Public Radio. He was not prepared to offer any additional details on the development of the app, leaving it unclear whether the tool will be available to residents when Boston's vaccine mandate for indoor recreational venues takes effect in mid-January.

"It should be ready soon. I'd give you a hard date, but it's soon. It will be soon," Baker said.

Baker gave a nearly identical timetable of "soon" almost one month ago during a previous appearance on Boston Public Radio.

The app would provide a quick response, or QR, code for businesses or other third parties to scan in order to verify a person's vaccination status. Baker said in November the program would not be mandatory and could help groups or businesses that want to more easily screen for unvaccinated patrons or guests.

Boston Mayor Michelle Wu has directed that proof of vaccination be required for indoor, public spaces, such as movie theaters, gyms and restaurants. The phased rollout of Boston's mandate is scheduled to begin Jan. 15.

"A lot of people have asked us to create this so that they would have it and so they could download it. And we get it, we understand it, and we're working on it," Baker said.

Asked about the availability of rapid testing to detect COVID-19, Baker said he wishes the Food and Drug Administration would be more open to approval of rapid tests, which are currently available under emergency use authorization.

"The FDA needs to catch up a little bit with some of the evidence that's in the field about the effectiveness of these tests and the accuracy of these tests," Baker said.

The state has recently entered into a purchasing agreement with iHealth Labs to provide millions of rapid tests to communities around the state and to allow municipalities to buy their own supplies of rapid tests with federal funds.

Also during the program, Baker mentioned that he and his wife are generous tippers because they both once worked in the service industry. The governor said he worked as a bartender at the Oxford Ale House in Harvard Square. The venerable restaurant space at the corner of Church and Palmer streets that housed the Oxford Ale House was most recently home to the Border Cafe, which closed in February.