Update as of 5:38 AM UTC:

The Pardot login issues via "Log In with Salesforce" have been resolved.

Please contact Support at https://help.salesforce.com if you encounter any further issues. We sincerely regret any inconvenience you have experienced as a result of this incident.

The Salesforce Technology team is currently investigating an issue when logging into Pardot via "Log In with Salesforce" as of 9:48 PM UTC. Pardot users will still be able to login to pi.pardot.com via Pardot login credentials. Updates will be posted here as new information becomes available. We appreciate your patience while we continue to investigate the issue.