Add webauthn

app/controllers/sessions_controller.rb

@@ -1,7 +1,8 @@
 class SessionsController < ApplicationController
-  allow_unauthenticated_access only: %i[ new create verify_totp ]
+  allow_unauthenticated_access only: %i[ new create verify_totp webauthn_challenge webauthn_verify ]
   rate_limit to: 20, within: 3.minutes, only: :create, with: -> { redirect_to signin_path, alert: "Too many attempts. Try again later." }
   rate_limit to: 10, within: 3.minutes, only: :verify_totp, with: -> { redirect_to totp_verification_path, alert: "Too many attempts. Try again later." }
+  rate_limit to: 10, within: 3.minutes, only: [:webauthn_challenge, :webauthn_verify], with: -> { render json: { error: "Too many attempts. Try again later." }, status: :too_many_requests }
 
   def new
     # Redirect to signup if this is first run
@@ -118,6 +119,141 @@ class SessionsController < ApplicationController
     redirect_to active_sessions_path, notice: "Session revoked successfully."
   end
 
+  # WebAuthn authentication methods
+  def webauthn_challenge
+    email = params[:email]&.strip&.downcase
+
+    if email.blank?
+      render json: { error: "Email is required" }, status: :unprocessable_entity
+      return
+    end
+
+    user = User.find_by(email_address: email)
+
+    if user.nil? || !user.can_authenticate_with_webauthn?
+      render json: { error: "User not found or WebAuthn not available" }, status: :unprocessable_entity
+      return
+    end
+
+    # Store user ID in session for verification
+    session[:pending_webauthn_user_id] = user.id
+
+    # Store redirect URL if present
+    if params[:rd].present?
+      validated_url = validate_redirect_url(params[:rd])
+      session[:webauthn_redirect_url] = validated_url if validated_url
+    end
+
+    begin
+      # Generate authentication options
+      # The WebAuthn gem will handle base64url encoding automatically
+      options = WebAuthn::Credential.options_for_get(
+        allow: user.webauthn_credentials.pluck(:external_id),
+        user_verification: "preferred"
+      )
+
+      # Store challenge in session
+      session[:webauthn_challenge] = options.challenge
+
+      render json: options
+
+    rescue => e
+      Rails.logger.error "WebAuthn challenge generation error: #{e.message}"
+      render json: { error: "Failed to generate WebAuthn challenge" }, status: :internal_server_error
+    end
+  end
+
+  def webauthn_verify
+    # Get pending user from session
+    user_id = session[:pending_webauthn_user_id]
+    unless user_id
+      render json: { error: "Session expired. Please try again." }, status: :unprocessable_entity
+      return
+    end
+
+    user = User.find_by(id: user_id)
+    unless user
+      session.delete(:pending_webauthn_user_id)
+      render json: { error: "Session expired. Please try again." }, status: :unprocessable_entity
+      return
+    end
+
+    # Get the credential and assertion from params
+    credential_data = params[:credential]
+    if credential_data.blank?
+      render json: { error: "Credential data is required" }, status: :unprocessable_entity
+      return
+    end
+
+    # Get the challenge from session
+    challenge = session.delete(:webauthn_challenge)
+
+    if challenge.blank?
+      render json: { error: "Invalid or expired session" }, status: :unprocessable_entity
+      return
+    end
+
+    begin
+      # Decode the credential response
+      webauthn_credential = WebAuthn::Credential.from_get(credential_data)
+
+      # Find the stored credential
+      external_id = Base64.urlsafe_encode64(webauthn_credential.id)
+      stored_credential = user.webauthn_credential_for(external_id)
+
+      if stored_credential.nil?
+        render json: { error: "Credential not found" }, status: :unprocessable_entity
+        return
+      end
+
+      # Verify the assertion
+      stored_public_key = Base64.urlsafe_decode64(stored_credential.public_key)
+      webauthn_credential.verify(
+        challenge,
+        public_key: stored_public_key,
+        sign_count: stored_credential.sign_count
+      )
+
+      # Check for suspicious sign count (possible clone)
+      if stored_credential.suspicious_sign_count?(webauthn_credential.sign_count)
+        Rails.logger.warn "Suspicious WebAuthn sign count for user #{user.id}, credential #{stored_credential.id}"
+        # You might want to notify admins or temporarily disable the credential
+      end
+
+      # Update credential usage
+      stored_credential.update_usage!(
+        sign_count: webauthn_credential.sign_count,
+        ip_address: request.remote_ip,
+        user_agent: request.user_agent
+      )
+
+      # Clean up session
+      session.delete(:pending_webauthn_user_id)
+      if session[:webauthn_redirect_url].present?
+        session[:return_to_after_authenticating] = session.delete(:webauthn_redirect_url)
+      end
+
+      # Create session
+      start_new_session_for user
+
+      render json: {
+        success: true,
+        redirect_to: after_authentication_url,
+        message: "Signed in successfully with passkey"
+      }
+
+    rescue WebAuthn::Error => e
+      Rails.logger.error "WebAuthn verification error: #{e.message}"
+      render json: { error: "Authentication failed: #{e.message}" }, status: :unprocessable_entity
+    rescue JSON::ParserError => e
+      Rails.logger.error "WebAuthn JSON parsing error: #{e.message}"
+      render json: { error: "Invalid credential format" }, status: :unprocessable_entity
+    rescue => e
+      Rails.logger.error "Unexpected WebAuthn verification error: #{e.class} - #{e.message}"
+      render json: { error: "An unexpected error occurred" }, status: :internal_server_error
+    end
+  end
+
   private
 
   def validate_redirect_url(url)