Merge pull request #59495 from ericchiang/client-auth-exec

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

 client-go: add an exec-based client auth provider

Updates https://github.com/kubernetes/features/issues/541
Implements https://github.com/kubernetes/community/pull/1503
Closes https://github.com/kubernetes/kubernetes/issues/57164

```release-note
client-go: alpha support for exec-based credential providers
```

/sig auth
/kind feature

Kubernetes-commit: cb9d6b51556a1677f262e35e4aded0051c424818

vendor/k8s.io/client-go/tools/clientcmd/client_config.go

@@ -241,6 +241,9 @@ func (config *DirectClientConfig) getUserIdentificationPartialConfig(configAuthI
 		mergedConfig.AuthProvider = configAuthInfo.AuthProvider
 		mergedConfig.AuthConfigPersister = persistAuthConfig
 	}
+	if configAuthInfo.Exec != nil {
+		mergedConfig.ExecProvider = configAuthInfo.Exec
+	}
 
 	// if there still isn't enough information to authenticate the user, try prompting
 	if !canIdentifyUser(*mergedConfig) && (fallbackReader != nil) {
@@ -291,7 +294,8 @@ func canIdentifyUser(config restclient.Config) bool {
 	return len(config.Username) > 0 ||
 		(len(config.CertFile) > 0 || len(config.CertData) > 0) ||
 		len(config.BearerToken) > 0 ||
-		config.AuthProvider != nil
+		config.AuthProvider != nil ||
+		config.ExecProvider != nil
 }
 
 // Namespace implements ClientConfig