add MCP support

app/controllers/mcp_controller.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+class McpController < ActionController::API
+  before_action :authenticate_user!
+  before_action :verify_mcp_enabled!
+
+  before_action do
+    authorize!(:manage, :mcp)
+  end
+
+  def call
+    return head :ok if request.raw_post.blank?
+
+    body = JSON.parse(request.raw_post)
+
+    result = Mcp::HandleRequest.call(body, current_user, current_ability)
+
+    if result
+      render json: result
+    else
+      head :accepted
+    end
+  rescue CanCan::AccessDenied
+    render json: { jsonrpc: '2.0', id: nil, error: { code: -32_603, message: 'Forbidden' } }, status: :forbidden
+  rescue JSON::ParserError
+    render json: { jsonrpc: '2.0', id: nil, error: { code: -32_700, message: 'Parse error' } }, status: :bad_request
+  end
+
+  private
+
+  def authenticate_user!
+    render json: { error: 'Not authenticated' }, status: :unauthorized unless current_user
+  end
+
+  def verify_mcp_enabled!
+    return if Docuseal.multitenant?
+
+    return if AccountConfig.exists?(account_id: current_user.account_id,
+                                    key: AccountConfig::ENABLE_MCP_KEY,
+                                    value: true)
+
+    render json: { error: 'MCP is disabled' }, status: :forbidden
+  end
+
+  def current_user
+    @current_user ||= user_from_api_key
+  end
+
+  def user_from_api_key
+    token = request.headers['Authorization'].to_s[/\ABearer\s+(.+)\z/, 1]
+
+    return if token.blank?
+
+    sha256 = Digest::SHA256.hexdigest(token)
+
+    User.joins(:mcp_tokens).active.find_by(mcp_tokens: { sha256:, archived_at: nil })
+  end
+end