#40: Add basic AuthenticationService and missing UI tests.

* Add MockAuthenticationService and ServerSelectionUITests.
* Add tests covering the Authentication flow.

ElementX/Sources/Services/Client/ClientError.swift

@@ -0,0 +1,30 @@
+//
+//  ClientError.swift
+//  ElementX
+//
+//  Created by Doug on 30/06/2022.
+//  Copyright © 2022 Element. All rights reserved.
+//
+
+import Foundation
+import MatrixRustSDK
+
+enum MatrixErrorCode: String, CaseIterable {
+    case unknown = "M_UNKNOWN"
+    case userDeactivated = "M_USER_DEACTIVATED"
+    case forbidden = "M_FORBIDDEN"
+}
+
+extension ClientError {
+    var code: MatrixErrorCode {
+        guard case let .Generic(message) = self else { return .unknown }
+        
+        for code in MatrixErrorCode.allCases {
+            if message.contains(code.rawValue) {
+                return code
+            }
+        }
+        
+        return .unknown
+    }
+}