Yes, Magento 2 One Step Checkout Extension Allow Customer to Login on Checkout Page. If customer is not logged in, they can sign in from the sign-in button at the top right corner.

Read this guide on How to Configure One Step Checkout in Magento 2 to setup this extension.

Here are the few more resource to help you get most out of this Magento 2 One Step Checkout Extension.

• How to Install One Step Checkout Extension On Cloud Hosted Magento 2
• How to Add a New Step in Checkout Page in Magento 2
• How to Enable Guest Checkout in Magento 2
• How to Reduce Abandon Carts with Magento 2 One Step Checkout Extension
• How to Manage Fields in Magento 2 Checkout Page
• One Page Checkout vs Multi-Step Checkout – Which One’s for You
• Benefits of One Step Checkout Magento 2 Extension
• Abandoned Cart Vs Abandoned Checkout in Magento 2
• One-Page Checkout Strategies to Maximize Your eCommerce Sales
• Boost Conversion Rate with Magento 2 One-Step Checkout Extension
• How to Revamp Multi-Step Checkout Process to One-Step Checkout in Your Magento 2 Store
• 5 Tips to Optimize Your Checkout Experience with Magento 2 One Step Checkout extension