Error 'There was a problem with your authentication attempt' on log in to AppExchange

Error Description

Users may receive the following error when attempting to authenticate to the Salesforce AppExchange using their Salesforce credentials.

Error Message

There was a problem with your authentication attempt. Please try again. If you continue to encounter problems, contact your administrator

Additional Symptom

In some cases, users are redirected to the AppExchange but see a blank page. The URL will contain:

appexchange.salesforce.com/partnerCommunityError?ErrorCode=Remote_Error&ErrorDescription=OAUTH_APP_BLOCKED

Root Cause

This error occurs because the AppExchange Connected App has been blocked in your Salesforce org's OAuth settings. A Salesforce Administrator must unblock it.