Fix connecting to OpenVPN when failedto fetch auth certificate [VPNWIN-829]

Author: mindaugasveblauskas

src/ProtonVPN.App/Vpn/VpnCredentialProvider.cs

@@ -20,6 +20,7 @@
 using System.Threading.Tasks;
 using ProtonVPN.Common.Abstract;
 using ProtonVPN.Common.Extensions;
+using ProtonVPN.Common.Networking;
 using ProtonVPN.Common.Vpn;
 using ProtonVPN.Core.Auth;
 using ProtonVPN.Core.Models;
@@ -51,7 +52,7 @@ public async Task<Result<VpnCredentials>> Credentials()
             User user = _userStorage.User();
 
             AuthCredential authCredential = await _authCredentialManager.GenerateAsync();
-            if (authCredential.CertificatePem.IsNullOrEmpty())
+            if (_appSettings.GetProtocol() == VpnProtocol.WireGuard && authCredential.CertificatePem.IsNullOrEmpty())
             {
                 return Result.Fail<VpnCredentials>();
             }

src/ProtonVPN.Common/Vpn/VpnCredentials.cs

@@ -27,7 +27,6 @@ public readonly struct VpnCredentials
         public VpnCredentials(string username, string password, string clientCertPem, AsymmetricKeyPair clientKeyPair)
             : this(username, password)
         {
-            Ensure.NotEmpty(clientCertPem, nameof(clientCertPem));
             Ensure.NotNull(clientKeyPair, nameof(clientKeyPair));
 
             ClientCertPem = clientCertPem;

src/ProtonVPN.Vpn/Connection/BestPortWrapper.cs

@@ -21,6 +21,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using ProtonVPN.Common;
+using ProtonVPN.Common.Extensions;
 using ProtonVPN.Common.Logging;
 using ProtonVPN.Common.Threading;
 using ProtonVPN.Common.Vpn;
@@ -121,8 +122,11 @@ private VpnCredentials GetCredentials(IVpnEndpoint endpoint)
             }
 
             string username = $"{_vpnCredentials.Username}+b:{endpoint.Server.Label}";
-            return new VpnCredentials(username, _vpnCredentials.Password, _vpnCredentials.ClientCertPem,
-                _vpnCredentials.ClientKeyPair);
+
+            return _vpnCredentials.ClientCertPem.IsNullOrEmpty() || _vpnCredentials.ClientKeyPair == null
+                ? new VpnCredentials(username, _vpnCredentials.Password)
+                : new VpnCredentials(username, _vpnCredentials.Password, _vpnCredentials.ClientCertPem,
+                    _vpnCredentials.ClientKeyPair);
         }
 
         private async void DelayedDisconnect(CancellationToken cancellationToken)