Feature request: don't ask for TouchID if OS doesn't require it

[joy13975]

TouchID is not required again by MacOS after a previous successful auth within 5min.

Currently, keymaster asks for TouchID every single time, and it can be quite annoying if chaining it with higher high frequency commands.

Request: please add session keeping to skip TouchID if within 5min of previous successful auth.

Will put up a PR after #4 is merged because the changes are stacked.