feat(authentication): support for exec kube config

Sources/SwiftkubeClient/Config/KubernetesClientConfig.swift

@@ -336,6 +336,72 @@ private extension AuthInfo {
 		} catch {
 			logger?.warning("Error initializing authentication from client certificate: \(error)")
 		}
+
+		#if os(Linux) || os(macOS)
+			do {
+				if let exec {
+					let outputData = try run(command: exec.command, arguments: exec.args)
+
+					let decoder = JSONDecoder()
+					decoder.dateDecodingStrategy = .iso8601
+					let credential = try decoder.decode(ExecCredential.self, from: outputData)
+
+					return .bearer(token: credential.status.token)
+				}
+			} catch {
+				logger?.warning("Error initializing authentication from exec \(error)")
+			}
+		#endif
 		return nil
 	}
 }
+
+// MARK: - ExecCredential
+
+// It seems that AWS doesn't implement properly the model for client.authentication.k8s.io/v1beta1
+// Acordingly with the doc https://kubernetes.io/docs/reference/config-api/client-authentication.v1beta1/
+// ExecCredential.Spec.interactive is required as long as the ones in the Status object.
+internal struct ExecCredential: Decodable {
+	let apiVersion: String
+	let kind: String
+	let spec: Spec
+	let status: Status
+}
+
+internal extension ExecCredential {
+	struct Spec: Decodable {
+		let cluster: Cluster?
+		let interactive: Bool?
+	}
+
+	struct Status: Decodable {
+		let expirationTimestamp: Date
+		let token: String
+		let clientCertificateData: String?
+		let clientKeyData: String?
+	}
+}
+
+#if os(Linux) || os(macOS)
+	internal func run(command: String, arguments: [String]? = nil) throws -> Data {
+		func run(_ command: String, _ arguments: [String]?) throws -> Data {
+			let task = Process()
+			task.executableURL = URL(fileURLWithPath: command)
+			task.arguments = arguments
+
+			let pipe = Pipe()
+			task.standardOutput = pipe
+
+			try task.run()
+
+			return pipe.fileHandleForReading.availableData
+		}
+
+		func resolve(command: String) throws -> String {
+			try String(decoding:
+				run("/usr/bin/which", ["\(command)"]), as: UTF8.self).trimmingCharacters(in: .whitespacesAndNewlines)
+		}
+
+		return try run(resolve(command: command), arguments)
+	}
+#endif