enhance: support client certificates for mutual TLS (#1273)

Add `runner.client_cert_file` and `runner.client_key_file` for Gitea instances that require mutual TLS. The runner presents the certificate on its RPCs, job summary uploads, and the action, reusable workflow and `builtin:checkout` clones from the instance. The files are read on use, so renewed certificates apply without a restart. Job steps do not get them. An incomplete or mismatched pair fails startup.

Clones now decide the token, client certificate and `runner.insecure` with one host check, which also gives reusable workflow clones the TLS settings they lacked. `runner.insecure` still only covers the registered address.

Fixes: https://gitea.com/gitea/runner/issues/321
Co-authored-by: silverwind <[email protected]>
Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1273
Reviewed-by: silverwind <[email protected]>
Co-authored-by: bircni <[email protected]>

act/common/git/git.go

@@ -168,7 +168,8 @@ type NewGitCloneExecutorInput struct {
 	Quiet bool
 
 	// For Gitea
-	InsecureSkipTLS bool
+	InsecureSkipTLS               bool
+	ClientCertFile, ClientKeyFile string // PEM, absolute as git runs in other directories
 }
 
 // CloneIfRequired reports whether an existing local clone was reused.
@@ -367,6 +368,9 @@ func runGit(ctx context.Context, dir string, input *NewGitCloneExecutorInput, ar
 	config := []string{"core.autocrlf=false", "core.eol=lf"} // keep action files LF
 	if input != nil {
 		config = append(config, RemoteConfig(input.Token, input.InsecureSkipTLS)...)
+		if input.ClientCertFile != "" {
+			config = append(config, "http.sslCert="+input.ClientCertFile, "http.sslKey="+input.ClientKeyFile)
+		}
 	}
 	if dir != "" {
 		args = append([]string{"-C", dir}, args...)