Add support for .p12 certificate files

[cn0238]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 54.28%. Comparing base (15edb67) to head (d46ffed).
⚠️ Report is 61 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/internal/token/clientcertcredential.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #649      +/-   ##
==========================================
- Coverage   63.43%   54.28%   -9.16%     
==========================================
  Files          37       42       +5     
  Lines        2210     2347     +137     
==========================================
- Hits         1402     1274     -128     
- Misses        733      974     +241     
- Partials       75       99      +24     

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[weinong]

@cn0238 can you sign the commit plz?

[cn0238]

@cn0238 can you sign the commit plz?

@weinong updated!

[weinong]

LGTM

[weinong]

@cn0238 are you able to sign the commit?