Introduce "tart logout" command (#583)

* Introduce "tart logout"

* tart login: introduce --no-validate

Sources/tart/Commands/Login.swift

@@ -17,6 +17,9 @@ struct Login: AsyncParsableCommand {
   @Flag(help: "connect to the OCI registry via insecure HTTP protocol")
   var insecure: Bool = false
 
+  @Flag(help: "skip validation of the registry's credentials before logging-in")
+  var noValidate: Bool = false
+
   func validate() throws {
     let usernameProvided = username != nil
     let passwordProvided = passwordStdin
@@ -45,12 +48,14 @@ struct Login: AsyncParsableCommand {
       host: (user, password)
     ])
 
-    do {
-      let registry = try Registry(host: host, namespace: "", insecure: insecure,
-                                  credentialsProviders: [credentialsProvider])
-      try await registry.ping()
-    } catch {
-      throw RuntimeError.InvalidCredentials("invalid credentials: \(error)")
+    if !noValidate {
+      do {
+        let registry = try Registry(host: host, namespace: "", insecure: insecure,
+                                    credentialsProviders: [credentialsProvider])
+        try await registry.ping()
+      } catch {
+        throw RuntimeError.InvalidCredentials("invalid credentials: \(error)")
+      }
     }
 
     try KeychainCredentialsProvider().store(host: host, user: user, password: password)

Sources/tart/Commands/Logout.swift

@@ -0,0 +1,14 @@
+import ArgumentParser
+import Dispatch
+import SwiftUI
+
+struct Logout: AsyncParsableCommand {
+  static var configuration = CommandConfiguration(abstract: "Logout from a registry")
+
+  @Argument(help: "host")
+  var host: String
+
+  func run() async throws {
+    try KeychainCredentialsProvider().remove(host: host)
+  }
+}

Sources/tart/Credentials/KeychainCredentialsProvider.swift

@@ -61,6 +61,24 @@ class KeychainCredentialsProvider: CredentialsProvider {
       throw CredentialsProviderError.Failed(message: "Keychain failed to find item: \(status.explanation())")
     }
   }
+
+  func remove(host: String) throws {
+    let query: [String: Any] = [kSecClass as String: kSecClassInternetPassword,
+                                kSecAttrServer as String: host,
+                                kSecAttrLabel as String: "Tart Credentials",
+    ]
+
+    let status = SecItemDelete(query as CFDictionary)
+
+    switch status {
+    case errSecSuccess:
+      return
+    case errSecItemNotFound:
+      return
+    default:
+      throw CredentialsProviderError.Failed(message: "Failed to remove Keychain item(s): \(status.explanation())")
+    }
+  }
 }
 
 extension OSStatus {

Sources/tart/Root.swift

@@ -16,6 +16,7 @@ struct Root: AsyncParsableCommand {
       Get.self,
       List.self,
       Login.self,
+      Logout.self,
       IP.self,
       Pull.self,
       Push.self,