Remove deprecated selfLink dependency

[int128]

This will remove dependency of deprecated selfLink field which will be removed in Kubernetes v1.20.0. Fix #89.

[codecov-commenter]

Codecov Report

Merging #93 into master will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   83.17%   83.33%   +0.15%     
==========================================
  Files           1        1              
  Lines         107      108       +1     
==========================================
+ Hits           89       90       +1     
  Misses         10       10              
  Partials        8        8              

Impacted Files	Coverage Δ
pkg/authproxy/auth_proxy.go	83.33% <100.00%> (+0.15%)	⬆️

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