Docusign effectively does this with all of its integrations. If you run on Salesforce, it's really well integrated. And if not, they have a great API. You can programmatically generate an https link and send that to your customers as part of your existing workflow. You email them a link or even just open up a new tab / overlay a browser. They can log in with various SSOs, they sign the form, then come back to the next stage in the workflow.

Edit: see https://www.docusign.com/products/apis