feat: add TimeFunc provides the current time.

[appleboy]

fix #65

[codecov-io]

Codecov Report

Merging #67 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
+ Coverage   96.27%   96.31%   +0.04%     
==========================================
  Files           1        1              
  Lines         161      163       +2     
==========================================
+ Hits          155      157       +2     
  Misses          4        4              
  Partials        2        2

Impacted Files	Coverage Δ
auth_jwt.go	96.31% <100%> (+0.04%)	⬆️

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