fix: set tls config while retaining other fields from default http transport

[nianyush]

Signed-off-by: Nianyu Shen xiaoyu9964@gmail.com

Summary

original issue #3269
Proxy from environment variable is not respected while setting insecure true.
At

cosign/cmd/cosign/cli/options/registry.go

Line 154 in 87c08b0

opts = append(opts, remote.WithTransport(&http.Transport{TLSClientConfig: tlsConfig}))

, its initializing an empty transport with only insecure set but those default behaviors from default transport is also gone. In this case, proxy value from envs is removed. The fix is to clone a default transport object and override the tlsconfig inside it.

Release Note

Documentation

[haydentherapper]

Thank you!

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 36.50%. Comparing base (2ef6022) to head (aa61fea).
Report is 276 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/cosign/cli/options/registry.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4007      +/-   ##
==========================================
- Coverage   40.10%   36.50%   -3.60%     
==========================================
  Files         155      209      +54     
  Lines       10044    13361    +3317     
==========================================
+ Hits         4028     4878     +850     
- Misses       5530     7862    +2332     
- Partials      486      621     +135     

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