Wallet & PSBT: Sign with seed or key (#840)

* Allow signing a PSBT with an extkey/wif or mnemonic seed

* reword things

* small text

BTCPayServer/Controllers/WalletsController.PSBT.cs

@@ -61,22 +61,25 @@ namespace BTCPayServer.Controllers
                 return View(vm);
             }
 
-            if (command == null)
+            switch (command)
             {
+                case null:
                     vm.Decoded = psbt.ToString();
                     vm.FileName = string.Empty;
                     return View(vm);
-            }
-            else if (command == "ledger")
-            {
+                case "ledger":
                     return ViewWalletSendLedger(psbt);
-            }
-            else if (command == "broadcast")
-            {
-                if (!psbt.IsAllFinalized() && !psbt.TryFinalize(out var errors))
+                case "seed":
+                    return RedirectToAction("SignWithSeed", new
                     {
+                        psbt = psbt.ToBase64(),
+                        walletId,
+                        send = false
+                    });
+                case "broadcast" when !psbt.IsAllFinalized() && !psbt.TryFinalize(out var errors):
                     return ViewPSBT(psbt, errors);
-                }
+                case "broadcast":
+                {
                     var transaction = psbt.ExtractTransaction();
                     try
                     {
@@ -92,17 +95,15 @@ namespace BTCPayServer.Controllers
                     }
                     return await RedirectToWalletTransaction(walletId, transaction);
                 }
-            else if (command == "combine")
-            {
+                case "combine":
                     ModelState.Remove(nameof(vm.PSBT));
                     return View(nameof(WalletPSBTCombine), new WalletPSBTCombineViewModel() { OtherPSBT = psbt.ToBase64() });
-            }
-            else if (command == "save-psbt")
-            {
+                case "save-psbt":
                     return FilePSBT(psbt, vm.FileName);
-            }
+                default:
                     return View(vm);
             }
+        }
 
         [HttpGet]
         [Route("{walletId}/psbt/ready")]

BTCPayServer/Controllers/WalletsController.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
 using System.Globalization;
 using System.Linq;
 using System.Net.WebSockets;
@@ -21,6 +22,7 @@ using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Identity;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.Extensions.Options;
 using NBitcoin;
 using NBitcoin.DataEncoders;
@@ -245,16 +247,22 @@ namespace BTCPayServer.Controllers
                 return View(vm);
             }
             derivationScheme.RebaseKeyPaths(psbt.PSBT);
-            if (command == "ledger")
+            switch (command)
             {
+                case "ledger":
                     return ViewWalletSendLedger(psbt.PSBT, psbt.ChangeAddress);
-            }
-            else if (command == "analyze-psbt")
+                case "seed":
+                    return RedirectToAction("SignWithSeed", new
                     {
+                        psbt = psbt.PSBT.ToBase64(),
+                        send = true
+                    });
+                case "analyze-psbt":
                     return ViewPSBT(psbt.PSBT, $"Send-{vm.Amount.Value}-{network.CryptoCode}-to-{destination[0].ToString()}.psbt");
-            }
+                default:
                     return View(vm);
             }
+        }
 
         private ViewResult ViewWalletSendLedger(PSBT psbt, BitcoinAddress hintChange = null)
         {
@@ -267,6 +275,90 @@ namespace BTCPayServer.Controllers
             });
         }
       
+        [HttpGet("{walletId}/psbt/seed")]
+        public IActionResult SignWithSeed([ModelBinder(typeof(WalletIdModelBinder))]
+            WalletId walletId,string psbt, bool send)
+        {
+            return View(new SignWithSeedViewModel()
+            {
+                PSBT = psbt,
+                Send = send
+            });
+        }
+
+        [HttpPost("{walletId}/psbt/seed")]
+        public async Task<IActionResult> SignWithSeed([ModelBinder(typeof(WalletIdModelBinder))]
+            WalletId walletId, SignWithSeedViewModel viewModel)
+        {
+            if (!ModelState.IsValid)
+            {
+                return View(viewModel);
+            }
+            var network = NetworkProvider.GetNetwork(walletId.CryptoCode);
+            if (network == null)
+                throw new FormatException("Invalid value for crypto code");
+            var isMnemonic = false;
+            var isExtKey = false;
+            ExtKey extKey = null;
+            try
+            {
+                var mnemonic = new Mnemonic(viewModel.SeedOrKey);
+                isMnemonic = true;
+                extKey = mnemonic.DeriveExtKey(viewModel.Passphrase);
+            }
+            catch (Exception)
+            {
+            }
+
+            if (!isMnemonic)
+            {
+                try
+                {
+                    extKey = ExtKey.Parse(viewModel.SeedOrKey, network.NBitcoinNetwork);
+                    isExtKey = true;
+                }
+                catch (Exception)
+                {
+                }
+            }
+
+            if (!isMnemonic && !isExtKey)
+            {
+                ModelState.AddModelError(nameof(viewModel.SeedOrKey),
+                    "Seed or Key was not in a valid format. It is either the 12/24 words or starts with xprv");
+            }
+
+            var psbt = PSBT.Parse(viewModel.PSBT, network.NBitcoinNetwork);
+
+            if (!psbt.IsReadyToSign())
+            {
+                ModelState.AddModelError(nameof(viewModel.PSBT), "PSBT is not ready to be signed");
+            }
+
+            if (!ModelState.IsValid)
+            {
+                return View(viewModel);
+            }
+
+
+            var signedpsbt = psbt.SignAll(extKey);
+
+            if (viewModel.Send)
+            {
+                return await WalletPSBTReady(walletId, new WalletPSBTReadyViewModel()
+                {
+                    PSBT = signedpsbt.ToBase64()
+                }, "broadcast");
+            }
+
+            return RedirectToAction("WalletPSBTReady", new
+            {
+                walletId,
+                psbt = signedpsbt.ToBase64()
+            });
+
+        }      
+        
         private IDestination[] ParseDestination(string destination, Network network)
         {
             try

BTCPayServer/Models/WalletViewModels/SignWithSeedViewModel.cs

@@ -0,0 +1,17 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace BTCPayServer.Models.WalletViewModels
+{
+    public class SignWithSeedViewModel
+    {
+        [Required]
+        public string PSBT { get; set; }
+        [Required][Display(Name = "Seed(12/24 word mnemonic seed) Or HD private key(xprv...)")]
+        public string SeedOrKey { get; set; }
+
+        [Display(Name = "Optional seed passphrase")]
+        public string Passphrase { get; set; }
+
+        public bool Send { get; set; }
+    }
+}

BTCPayServer/Views/Wallets/SignWithSeed.cshtml

@@ -0,0 +1,35 @@
+@model SignWithSeedViewModel
+@{
+    Layout = "../Shared/_NavLayout.cshtml";
+    ViewData["Title"] = "Sign PSBT With an HD private key or mnemonic seed";
+    ViewData.SetActivePageAndTitle(Model.Send ? WalletsNavPages.Send : WalletsNavPages.PSBT);
+}
+
+<div class="row">
+    <div class="col-md-10">
+        <div asp-validation-summary="All" class="text-danger"></div>
+        <form method="post">
+            
+            <input type="hidden" asp-for="PSBT"/>
+            <input type="hidden" asp-for="Send"/>
+            <div class="form-group">
+                <label asp-for="SeedOrKey"></label>
+                <input asp-for="SeedOrKey" class="form-control"/>
+                <span asp-validation-for="SeedOrKey" class="text-danger"></span>
+            </div>
+
+            <div class="form-group">
+                <label asp-for="Passphrase"></label>
+                <input asp-for="Passphrase" class="form-control"/>
+                <span asp-validation-for="Passphrase" class="text-danger"></span>
+            </div>
+            <button type="submit" class="btn btn-primary">Sign</button>
+        </form>
+    </div>
+</div>
+
+@section Scripts {
+    <link rel="stylesheet" href="~/vendor/highlightjs/default.min.css">
+    <script src="~/vendor/highlightjs/highlight.min.js"></script>
+    <script>hljs.initHighlightingOnLoad();</script>
+}

BTCPayServer/Views/Wallets/WalletPSBT.cshtml

@@ -35,6 +35,7 @@
                         <div class="dropdown-menu" aria-labelledby="SendMenu">
                             <button name="command" type="submit" class="dropdown-item" value="ledger">... your Ledger Wallet device</button>
                             <button name="command" type="submit" class="dropdown-item" value="save-psbt">... a wallet supporting PSBT files</button>
+                            <button name="command" type="submit" class="dropdown-item" value="seed">... an HD private key or mnemonic seed</button>
                         </div>
                         <button name="command" type="submit" class="btn btn-secondary" value="broadcast">Broadcast</button>
                         <button name="command" type="submit" class="btn btn-secondary" value="combine">Combine with another PSBT</button>

BTCPayServer/Views/Wallets/WalletSend.cshtml

@@ -89,6 +89,7 @@
                     </button>
                     <div class="dropdown-menu" aria-labelledby="SendMenu">
                         <button name="command" type="submit" class="dropdown-item" value="ledger">... your Ledger Wallet device</button>
+                        <button name="command" type="submit" class="dropdown-item" value="seed">... an HD private key or mnemonic seed</button>
                         <button name="command" type="submit" class="dropdown-item" value="analyze-psbt">... a wallet supporting PSBT</button>
                     </div>
                 </div>