Exception: Sitecore.XConnect.XdbCollectionUnavailableException
Message: The HTTP response was not successful: Unauthorized
Source: Sitecore.Xdb.Common.WebWas getting the error above during our SSO process. The solution for me was changing the SSL settings in IIS for the xconnect website from Ignore to Accept.
After hours of checking certificates and logs and trying all other options. This finally worked for me. Thanks a ton for Posting !