Refactor Nostr settings/connect

* Use NIP-42 auth event instead of short text note
* Verify event ID and signature using the nostr gem instead of custom code

app/controllers/application_controller.rb

@@ -63,4 +63,9 @@ class ApplicationController < ActionController::Base
     @fetch_balance_retried = true
     lndhub_fetch_balance
   end
+
+  def nostr_event_from_params
+    params.permit!
+    params[:signed_event].to_h.symbolize_keys
+  end
 end

app/controllers/settings_controller.rb

@@ -87,25 +87,27 @@ class SettingsController < ApplicationController
   end
 
   def set_nostr_pubkey
-    signed_event = nostr_event_params[:signed_event].to_h.symbolize_keys
+    signed_event = Nostr::Event.new(**nostr_event_from_params)
 
-    is_valid_id  = NostrManager::ValidateId.call(event: signed_event)
-    is_valid_sig = NostrManager::VerifySignature.call(event: signed_event)
-    is_correct_content = signed_event[:content] == "Connect my public key to #{current_user.address} (confirmation #{session[:shared_secret]})"
+    is_valid_sig  = signed_event.verify_signature
+    is_valid_auth = NostrManager::VerifyAuth.call(
+      event: signed_event,
+      challenge: session[:shared_secret]
+    )
 
-    unless is_valid_id && is_valid_sig && is_correct_content
+    unless is_valid_sig && is_valid_auth
       flash[:alert] = "Public key could not be verified"
       http_status :unprocessable_entity and return
     end
 
-    user_with_pubkey = LdapManager::FetchUserByNostrKey.call(pubkey: signed_event[:pubkey])
+    user_with_pubkey = LdapManager::FetchUserByNostrKey.call(pubkey: signed_event.pubkey)
 
     if user_with_pubkey.present? && (user_with_pubkey != current_user)
       flash[:alert] = "Public key already in use for a different account"
       http_status :unprocessable_entity and return
     end
 
-    LdapManager::UpdateNostrKey.call(dn: current_user.dn, pubkey: signed_event[:pubkey])
+    LdapManager::UpdateNostrKey.call(dn: current_user.dn, pubkey: signed_event.pubkey)
     session[:shared_secret] = nil
 
     flash[:success] = "Public key verification successful"
@@ -160,12 +162,6 @@ class SettingsController < ApplicationController
       params.require(:user).permit(:current_password)
     end
 
-    def nostr_event_params
-      params.permit(signed_event: [
-        :id, :pubkey, :created_at, :kind, :content, :sig, tags: []
-      ])
-    end
-
     def generate_email_password
       characters = [('a'..'z'), ('A'..'Z'), (0..9)].map(&:to_a).flatten
       SecureRandom.random_bytes(16).each_byte.map { |b| characters[b % characters.length] }.join

app/javascript/controllers/settings/nostr_pubkey_controller.js

@@ -3,7 +3,12 @@ import { Controller } from "@hotwired/stimulus"
 // Connects to data-controller="settings--nostr-pubkey"
 export default class extends Controller {
   static targets = [ "noExtension", "setPubkey", "pubkeyBech32Input" ]
-  static values  = { userAddress: String, pubkeyHex: String, sharedSecret: String }
+  static values  = {
+    userAddress: String,
+    pubkeyHex: String,
+    site: String,
+    sharedSecret: String
+  }
 
   connect () {
     if (window.nostr) {
@@ -19,11 +24,15 @@ export default class extends Controller {
     this.setPubkeyTarget.disabled = true
 
     try {
+      // Auth based on NIP-42
       const signedEvent = await window.nostr.signEvent({
         created_at: Math.floor(Date.now() / 1000),
-        kind: 1,
-        tags: [],
-        content: `Connect my public key to ${this.userAddressValue} (confirmation ${this.sharedSecretValue})`
+        kind: 22242,
+        tags: [
+          ["site", this.siteValue],
+          ["challenge", this.sharedSecretValue]
+        ],
+        content: ""
       })
 
       const res = await fetch("/settings/set_nostr_pubkey", {

app/services/nostr_manager/validate_id.rb

@@ -1,11 +0,0 @@
-module NostrManager
-  class ValidateId < NostrManagerService
-    def initialize(event:)
-      @event = Nostr::Event.new(**event)
-    end
-
-    def call
-      @event.id == Digest::SHA256.hexdigest(JSON.generate(@event.serialize))
-    end
-  end
-end

app/services/nostr_manager/verify_auth.rb

@@ -0,0 +1,17 @@
+module NostrManager
+  class VerifyAuth < NostrManagerService
+    def initialize(event:, challenge:)
+      @event = event
+      @challenge_expected = challenge
+      @site_expected = Setting.accounts_domain
+    end
+
+    def call
+      site_given      = @event.tags.find{|t| t[0] == "site"}[1]
+      challenge_given = @event.tags.find{|t| t[0] == "challenge"}[1]
+
+      site_given == @site_expected &&
+      challenge_given == @challenge_expected
+    end
+  end
+end

app/services/nostr_manager/verify_signature.rb

@@ -1,17 +0,0 @@
-module NostrManager
-  class VerifySignature < NostrManagerService
-    def initialize(event:)
-      @event = Nostr::Event.new(**event)
-    end
-
-    def call
-      Schnorr.check_sig!(
-        [@event.id].pack('H*'),
-        [@event.pubkey].pack('H*'),
-        [@event.sig].pack('H*')
-      )
-    rescue Schnorr::InvalidSignatureError
-      false
-    end
-  end
-end

app/views/settings/_nostr.html.erb

@@ -3,6 +3,7 @@
   <h4 class="mb-0">Public Key</h4>
   <div data-controller="settings--nostr-pubkey"
        data-settings--nostr-pubkey-user-address-value="<%= current_user.address %>"
+       data-settings--nostr-pubkey-site-value="<%= Setting.accounts_domain %>"
        data-settings--nostr-pubkey-shared-secret-value="<%= session[:shared_secret] %>"
        data-settings--nostr-pubkey-pubkey-hex-value="<%= current_user.nostr_pubkey %>">