Follow-up from "Support mutual TLS when calling the GitLab API"

The following discussion from !978 (merged) should be addressed:

Implementation guide

• @jaime started a discussion: (+3 comments)

  All these fields are being re-used so we risk having some value change in one transport but not others. Can we simply reuse the NewTransport function and just modify the TLSClientConfig with the config?. For example

  diff --git a/internal/httptransport/transport.go b/internal/httptransport/transport.go
  index da38e0a9..f90cfd06 100644
  --- a/internal/httptransport/transport.go
  +++ b/internal/httptransport/transport.go
  @@ -44,8 +44,7 @@ func NewTransport() *http.Transport {
   		DialTLS: func(network, addr string) (net.Conn, error) {
   			return tls.Dial(network, addr, &tls.Config{RootCAs: pool(), MinVersion: tls.VersionTLS12})
   		},
  -		TLSClientConfig: &tls.Config{MinVersion: tls.VersionTLS12}, // set MinVersion to fix gosec: G402
  -		Proxy:           http.ProxyFromEnvironment,
  +		Proxy: http.ProxyFromEnvironment,
   		// overrides the DefaultMaxIdleConnsPerHost = 2
   		MaxIdleConns:        100,
   		MaxIdleConnsPerHost: 100,
  @@ -86,21 +85,10 @@ func NewTransportWithClientCert(clientCfg config.HTTPClientCfg) *http.Transport
   		tlsConfig.Certificates = clientCfg.Certs
   	}
  
  -	return &http.Transport{
  -		DialTLS: func(network, addr string) (net.Conn, error) {
  -			return tls.Dial(network, addr, tlsConfig)
  -		},
  -		TLSClientConfig: tlsConfig,
  -		Proxy:           http.ProxyFromEnvironment,
  -		// overrides the DefaultMaxIdleConnsPerHost = 2
  -		MaxIdleConns:        100,
  -		MaxIdleConnsPerHost: 100,
  -		IdleConnTimeout:     90 * time.Second,
  -		// Set more timeouts https://gitlab.com/gitlab-org/gitlab-pages/-/issues/495
  -		TLSHandshakeTimeout:   10 * time.Second,
  -		ResponseHeaderTimeout: 15 * time.Second,
  -		ExpectContinueTimeout: 15 * time.Second,
  -	}
  +	t := NewTransport()
  +	t.TLSClientConfig = tlsConfig
  +
  +	return t
   }