DocuSign Insight-SSO login in legacy ATN plugin fails with "The password has exceeded 512 bytes"

Issue

An attempt to login via SSO to the legacy VSTO (installed via msi installer), ATN plugin throws blank browser page and following dialog box:

“12.02.2020 10:03:52 Error Failed to acquire oAuth token.
The password has exceeded 512 bytes. GetOAuthTokenFailed MUNICH\ny00866”

Same user can login via SSO to Seal Discovery successfully.
Also it works for ATN installed as Office.js plugin (used for SealNow).
Issue was specific to MS Azure authentication, while it worked well for Google authentication.
 

Cause

When the token has been received, the VSTO ATN stores the string into the Windows Credentials Store for safe keeping. However, this storage area is restricted to 512 characters, which is sufficient space for storing a Google Auth token. However, Azure Ad auth tokens are much longer - too long to Windows Credentials Store. 

Solution

This issue is corrected in the latter ATN plugins starting with version 7.0.2.188