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]>

internal/app/run/runner.go

@@ -74,6 +74,7 @@ type Runner struct {
 	capabilities string
 
 	isolatedCacheContainer func() string
+	instanceTransport      http.RoundTripper
 
 	runningTasks            sync.Map
 	runningCount            atomic.Int64
@@ -140,6 +141,7 @@ func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client)
 		runHealthCheck: executeHealthCheck,
 	}
 	runner.isolatedCacheContainer = sync.OnceValue(runner.detectIsolatedCacheContainer)
+	runner.instanceTransport = client.NewTransport(cli.Address(), cfg.Runner.TLSConfig())
 	return runner
 }
 
@@ -626,6 +628,9 @@ func (r *Runner) run(ctx context.Context, task *runnerv1.Task, reporter *report.
 		ValidVolumes:                      r.cfg.Container.ValidVolumes,
 		SharedToolCache:                   r.cfg.Runner.ToolCacheMode == config.ToolCacheModeShared,
 		InsecureSkipTLS:                   r.cfg.Runner.Insecure,
+		ClientCertFile:                    r.cfg.Runner.ClientCertFile,
+		ClientKeyFile:                     r.cfg.Runner.ClientKeyFile,
+		InstanceTransport:                 r.instanceTransport,
 		RunnerName:                        r.name,
 		KubernetesPicker:                  r.kubernetesOptions,
 	}