Improve support for 'exec' credentials. (#774)

src/KubernetesClient/Authentication/ExecTokenProvider.cs

@@ -0,0 +1,52 @@
+using System.Diagnostics;
+using System.Net.Http.Headers;
+using System.Threading;
+using System.Threading.Tasks;
+using k8s.Exceptions;
+using k8s.KubeConfigModels;
+using Microsoft.Rest;
+
+namespace k8s.Authentication
+{
+    public class ExecTokenProvider : ITokenProvider
+    {
+        private readonly ExternalExecution exec;
+        private ExecCredentialResponse response;
+
+        public ExecTokenProvider(ExternalExecution exec)
+        {
+            this.exec = exec;
+        }
+
+        private bool NeedsRefresh()
+        {
+            if (response?.Status == null)
+            {
+                return true;
+            }
+
+            if (response.Status.Expiry == null)
+            {
+                return false;
+            }
+
+            return DateTime.UtcNow.AddSeconds(30) > response.Status.Expiry;
+        }
+
+        public async Task<AuthenticationHeaderValue> GetAuthenticationHeaderAsync(CancellationToken cancellationToken)
+        {
+            if (NeedsRefresh())
+            {
+                await RefreshToken().ConfigureAwait(false);
+            }
+
+            return new AuthenticationHeaderValue("Bearer", response.Status.Token);
+        }
+
+        private async Task RefreshToken()
+        {
+            response =
+                await Task.Run(() => KubernetesClientConfiguration.ExecuteExternalCommand(this.exec)).ConfigureAwait(false);
+        }
+    }
+}

src/KubernetesClient/KubeConfigModels/ExecCredentialResponse.cs

@@ -2,11 +2,27 @@ namespace k8s.KubeConfigModels
 {
     public class ExecCredentialResponse
     {
+        public class ExecStatus
+        {
+            #nullable enable
+            public DateTime? Expiry { get; set; }
+            public string? Token { get; set; }
+            public string? ClientCertificateData { get; set; }
+            public string? ClientKeyData { get; set; }
+            #nullable disable
+
+            public bool IsValid()
+            {
+                return (!string.IsNullOrEmpty(Token) ||
+                        (!string.IsNullOrEmpty(ClientCertificateData) && !string.IsNullOrEmpty(ClientKeyData)));
+            }
+        }
+
         [JsonPropertyName("apiVersion")]
         public string ApiVersion { get; set; }
         [JsonPropertyName("kind")]
         public string Kind { get; set; }
         [JsonPropertyName("status")]
-        public IDictionary<string, string> Status { get; set; }
+        public ExecStatus Status { get; set; }
     }
 }

src/KubernetesClient/KubernetesClientConfiguration.ConfigFile.cs

@@ -444,15 +444,21 @@ namespace k8s
                     throw new KubeConfigException("External command execution missing ApiVersion key");
                 }
 
-                var (accessToken, clientCertificateData, clientCertificateKeyData) = ExecuteExternalCommand(userDetails.UserCredentials.ExternalExecution);
-                AccessToken = accessToken;
+                var response = ExecuteExternalCommand(userDetails.UserCredentials.ExternalExecution);
+                AccessToken = response.Status.Token;
                 // When reading ClientCertificateData from a config file it will be base64 encoded, and code later in the system (see CertUtils.GeneratePfx)
                 // expects ClientCertificateData and ClientCertificateKeyData to be base64 encoded because of this. However the string returned by external
                 // auth providers is the raw certificate and key PEM text, so we need to take that and base64 encoded it here so it can be decoded later.
-                ClientCertificateData = clientCertificateData == null ? null : Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(clientCertificateData));
-                ClientCertificateKeyData = clientCertificateKeyData == null ? null : Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(clientCertificateKeyData));
+                ClientCertificateData = response.Status.ClientCertificateData == null ? null : Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(response.Status.ClientCertificateData));
+                ClientCertificateKeyData = response.Status.ClientKeyData == null ? null : Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(response.Status.ClientKeyData));
 
                 userCredentialsFound = true;
+
+                // TODO: support client certificates here too.
+                if (AccessToken != null)
+                {
+                    TokenProvider = new ExecTokenProvider(userDetails.UserCredentials.ExternalExecution);
+                }
             }
 
             if (!userCredentialsFound)
@@ -525,7 +531,7 @@ namespace k8s
         /// <returns>
         /// The token, client certificate data, and the client key data received from the external command execution
         /// </returns>
-        public static (string, string, string) ExecuteExternalCommand(ExternalExecution config)
+        public static ExecCredentialResponse ExecuteExternalCommand(ExternalExecution config)
         {
             if (config == null)
             {
@@ -562,18 +568,9 @@ namespace k8s
                         $"external exec failed because api version {responseObject.ApiVersion} does not match {config.ApiVersion}");
                 }
 
-                if (responseObject.Status.ContainsKey("token"))
+                if (responseObject.Status.IsValid())
                 {
-                    return (responseObject.Status["token"], null, null);
-                }
-                else if (responseObject.Status.ContainsKey("clientCertificateData"))
-                {
-                    if (!responseObject.Status.ContainsKey("clientKeyData"))
-                    {
-                        throw new KubeConfigException($"external exec failed missing clientKeyData field in plugin output");
-                    }
-
-                    return (null, responseObject.Status["clientCertificateData"], responseObject.Status["clientKeyData"]);
+                    return responseObject;
                 }
                 else
                 {

src/KubernetesClient/KubernetesClientConfiguration.InCluster.cs

@@ -24,7 +24,7 @@ namespace k8s
             var host = Environment.GetEnvironmentVariable("KUBERNETES_SERVICE_HOST");
             var port = Environment.GetEnvironmentVariable("KUBERNETES_SERVICE_PORT");
 
-            if (String.IsNullOrEmpty(host) || String.IsNullOrEmpty(port))
+            if (string.IsNullOrEmpty(host) || string.IsNullOrEmpty(port))
             {
                 return false;
             }