I have some questions:
1. I need to implement the following logic on C#: The customer signs the contract generated on our portal with your service.
Step 1. The website loads into your service pre-generated document with a place for a signature.
Step 2. We will show this document on our website special page, where the customer signs it.
Step 3. Copy of the signed document send by the mail to client.
So, we not need that client has account in your service. How realize get access token to our application?
2. On the test server, we have a self-signed certificate for ssl. Is it possible to use as a temporary redirect_url?
As per the mentioned workflow, you can first create a Widget either through web portal or using an API and can embed it in your website. Then, once it is being signed, you can access it by method getDocument(). Also, by default, once the document is signed, both the sender and signer would receive an email with copy of signed document and the signer doesn't need to have any E-Sign account.
Let me know if that helps.