Final Status: Engineers successfully updated the mismatched certificate throughout the affected environment. The issue has been successfully remediated.
User Experience: Affected users were unable to sign in to Yammer using the Single Sign-On (SSO) tool.
Customer Impact: The impact was specific to users who utilize the Azure identity provider for SSO authentication. Impact appears to have been limited throughout the duration of the incident.
Preliminary Root Cause: In an effort to ensure that Microsoft maintains the most invulnerable authentication standards, Microsoft Azure periodically updates their authentication certificates. A certificate mismatch between the Yammer and Azure environments prevented some customers from signing in to the Yammer service.