Implement Docusign OAuth provider

[denis-goncharenko]

This feature allows users to authenticate using their Docusign credentials. Tested in production service and works perfectly.

[kevinchalet]

Tested in production service and works perfectly.

Isn't https://account-d.docusign.com/ DocuSign's dev environment?

We'll need to add an Environment option to allow users to change the environment without having to replace each endpoint manually to use https://account.docusign.com/ instead of https://account-d.docusign.com/.

[denis-goncharenko]

Tested in production service and works perfectly.

Isn't https://account-d.docusign.com/ DocuSign's dev environment?

We'll need to add an Environment option to allow users to change the environment without having to replace each endpoint manually to use https://account.docusign.com/ instead of https://account-d.docusign.com/.

You are right. It's my fault I've just tested in prod and then in sandbox and forgot to change it.

I'll add the 'Environment' option.

[denis-goncharenko]

I've included the 'Environment' option to facilitate work with development and production environments. I have tested both options, and they work as expected.

[martincostello]

Could you update the version for 8.2.0 here please as we're adding a new provider?

AspNet.Security.OAuth.Providers/eng/Versions.props

Lines 5 to 6 in 5319292

	<MinorVersion>1</MinorVersion>
	<PatchVersion>1</PatchVersion>

Otherwise LGTM.

[denis-goncharenko]

Hello @martincostello! When are you planning to create NuGet packages for version 8.2.0?

[martincostello]

#910 is still WIP so assumed we'd do the release when that was finished too.