Walouh

I had the same issue, and overrided the behaviour of DocuSignClient.GenerateAccessToken. It is indeed related to the changes you mentionned (here : https://github.com/docusign/docusign-esign-csharp-client/commit/bbc7e3df590ff5a961fb3efc239405367d3bc380#diff-ba42f5f1289226fd9b2414cf211518bd5cdd7a81e4d5764fe74fb90ee6b2ada7R91) I only had to change the contentType...