Allow the app to be configured to bypass the server selection screen. (#4131)

* Make account provider configuration more flexible.

- Change defaultHomeserverAddress to an array of providers (needs UI).
- Add allowOtherAccountProviders to prevent the user from manually entering a provider.

* Refactor QR code scan failures into a common type.

* Validate scanned QR codes against the allowed account providers.

* Hide the login flow on the QR code screen when restricted.

ElementX/Sources/Services/Authentication/AuthenticationService.swift

@@ -36,7 +36,7 @@ class AuthenticationService: AuthenticationServiceProtocol {
         self.appHooks = appHooks
         
         // When updating these, don't forget to update the reset method too.
-        homeserverSubject = .init(LoginHomeserver(address: appSettings.defaultHomeserverAddress, loginMode: .unknown))
+        homeserverSubject = .init(LoginHomeserver(address: appSettings.accountProviders[0], loginMode: .unknown))
         flow = .login
     }
     
@@ -146,7 +146,7 @@ class AuthenticationService: AuthenticationServiceProtocol {
     }
     
     func reset() {
-        homeserverSubject.send(LoginHomeserver(address: appSettings.defaultHomeserverAddress, loginMode: .unknown))
+        homeserverSubject.send(LoginHomeserver(address: appSettings.accountProviders[0], loginMode: .unknown))
         flow = .login
         client = nil
     }

ElementX/Sources/Services/QRCode/QRCodeLoginService.swift

@@ -43,6 +43,16 @@ final class QRCodeLoginService: QRCodeLoginServiceProtocol {
             return .failure(.invalidQRCode)
         }
         
+        guard let scannedServerName = qrData.serverName() else {
+            MXLog.error("The QR code is from a device that is not yet signed in.")
+            return .failure(.deviceNotSignedIn)
+        }
+        
+        if !appSettings.allowOtherAccountProviders, !appSettings.accountProviders.contains(scannedServerName) {
+            MXLog.error("The scanned device's server is not allowed: \(scannedServerName)")
+            return .failure(.providerNotAllowed(scannedProvider: scannedServerName, allowedProviders: appSettings.accountProviders))
+        }
+        
         let listener = SDKListener { [weak self] progress in
             self?.qrLoginProgressSubject.send(progress)
         }

ElementX/Sources/Services/QRCode/QRCodeLoginServiceProtocol.swift

@@ -13,6 +13,7 @@ import MatrixRustSDK
 enum QRCodeLoginServiceError: Error {
     case failedLoggingIn
     case invalidQRCode
+    case providerNotAllowed(scannedProvider: String, allowedProviders: [String])
     case cancelled
     case connectionInsecure
     case declined