To have quickly or easily achieved a goal or gained access as desired, sometimes in a sexual manner.
In Like Flint was a sequel to the James Coburn movie
Our Man Flint and was a play on words from the original phrase "in like Flynn" that was coined by reporters about the time of the 1943 statutory rape trial of Errol Flynn.
In like Flynn or
in like Flint mean the same thing and don't let some Nazi Fascist pick your allusion and allegory for you. Personally, I prefer "flint", even if your audience doesn't know who Errol Flynn and Derek Flint are, then at least word at least lends itself to a spark.
You can be "in like" anything you want it to be; in like Flynn, in like Flint, in like Bill Clinton...... take your pick! Hopefully, you've tailored phrasing to your audience.